NERVA starship shuttle or even SSTO

[EzinX]

So, alright. We've all seen the image of a hypothetical warp drive equipped spacecraft. Probably total science fantasy, but it sure looks pretty. Seeing that image, I immediately began to wonder : let's suppose you could build a spacecraft that vaguely resembles the rendering, with a working FTL warp drive, but other than the warp engine, you did not have any technology we cannot reasonably extrapolate from known principles and physics.

Again, this discussion is not about the warp engine. Let's just pretend it works, and suppose that you could travel 10s of light years in a matter of months. So you are out exploring, and you encounter a planet similar to the Earth in that it has a similar atmosphere composition, at least half the surface is water, and it has a surface gravity of 10 m/s^2. How convenient.

You are quite excited to land on that planet with a landing party and meet the alien <strike>women</strike> organisms up close and personal.

Fortunately, the wizards back at NASA have loaded up your starship with a vehicle capable of, at a minimum :

1. Taking off and landing from an earth like planet (in atmosphere, gravity, and element mix) without help from the ground with humans onboard

2. For an even harder challenge, it's an SSTO that must make orbit with no missing parts except fuel

What would the form of the vehicle even look like to pass a napkin test? This is, to me, a fascinating challenge.

Here's where I'm at so far.

Vehicle starts with a similar lifting body design to the space shuttle and various space-planes, but it has to be even larger than the space shuttle orbiter. It has a massive reactor in the back, similar to the one used by Project Pluto, but it's dual mode, capable of working to superheat both atmospheric gas and stored onboard hydrogen for thrust. There's a crew capsule in the very nose, protected by a shadow shield. (this is the main reason it has to be large : the larger it gets, the relative mass penalty for shielding against radiation from the reactor becomes smaller)

There's 7 main phases of flight.

1. Reentry - Vehicle uses similar mechanism to previous spaceplanes. Though it's quite rear-heavy from the reactor and it has mostly empty fuel tanks.

2. Soft Landing - Once it reaches cooler altitudes, damper doors over 2 turbine air intakes at the front of the vehicle are slid open. These are turbines powered by the reactor (via a hot-air power take-off turbine in the back and a long driveshaft) and they compress incident air and feed it to the reactor in the back. With sufficient power, you land this vehicle onto a calm patch of the ocean's surface on hydrofoil skis that deploy from the bottom.

3. Take off. After a stay on the ground, you have to start from 0 m/s to even get enough speed to get off the water. Good thing you have compressor turbines that can compress outside air to feed to the engine. You don't need a TWR of >1 to take off like a seaplane, maybe 0.3-0.4 or so will do it. (not certain how much skis reduce drag compared to tires on a runway). The moment you depart the water surface, you jettison the modules containing the skis and any floats.

4. Fueling. Once already in the air on nuclear thrust, you fly around for hours to days to fill your onboard fuel tanks. On an earth like planet, you do this by collecting water from the atmosphere with condenser coils, electrolyzing it for the hydrogen, then filling your onboard tanks with liquid hydrogen. Once you have full tanks, you jettison the modules containing the electrolysis equipment. You might have done this stage before takeoff if the atmospheric concentration of water is low.

5. Transition to ramjet flight. Faster and faster you go. Once you are going fast enough, you jettison the modules containing your main wings and the compressor turbines and all the equipment needed to drive them. The craft is now only flying due to nuclear ramjet thrust and the main fuselage, sans wings, is enough of a lifting body to stay in the air.

6. Transition to scramjet flight. You shed part of your ramjet air intake...at high speeds...leaving only a smaller intake for scramjet air.

7. To space. From extremely high altitude, and up to half orbital velocity, it's time to go to space today. Let's say you're going at 1/3 orbital velocity already, and your nuclear engine gives 1000 ISP when configured for hydrogen. So your scramjet is already going 2.6 km/second, and you need 6 km/second, even, plus a little margin. Half the mass of your remaining craft has to be fuel, stored as liquid hydrogen which is not very dense, and you've still got your crew compartment, radiation shield, and monster nuclear engine. If you had several modules to the nuclear engine, you could make this more efficient by dumping the extra modules later in the burn once you have shed enough weight in propellant. For bonus points, these modules would be optimized for handling atmospheric air, while the core would be designed with channels for liquid hydrogen.

8. Waiting in orbit. You need enough stuff working to wait in orbit. Your monster nuclear engine is still incredibly hot and dangerous, producing 1/3 of the many gigawatts of power it had to produce right up to engine cut off. Realistically you're gonna have to dump it, you don't have the mass budget for radiators to keep it cool once you're out of propellant. So you jettison the entire propulsion section, leaving just the crew capsule and enough batteries and life support on board to stay alive until the mothership picks you up.

Frankly, this design barely seems plausible on a napkin. Even if you posit incredible engineering talent, better than anyone who has ever lived, to develop this vehicle, I don't know if it could ever actually work.

If we're gonna land and take off with an intact vehicle we can use for another shuttle run, this isn't gonna work. What design could work? Once we send down the red-shirts to make sure it's safe, the captain is going to want to join them in the interspecies exchange with the alien women. So the shuttle needs to be able to ascend to orbit and pick him up.

Edited March 7, 2015 by EzinX

[Bill Phil]

So, an SSTO trumps a starship, huh?

[EzinX]

So, an SSTO trumps a starship, huh?

I'm assuming the starship is powered by pixie dust that ceases being magical when you get near a planet.

I see your point, though. At the tech level you needed to even get here in the first place, you have control of antimatter and also molecular manufacturing. Heck, you probably don't even need crew to reach the surface and return - you could just send landers, and have the crew personalities digitally take control of robots on the ground, uploading the changes in their memories after they are done exploring.

[Kibble]

I actually think the warship looks fairly unattractive. I'd take Saturn V over it any day!

[Nibb31]

I'm not sure what kind of input you are expecting from this thread. You seem to have it all figured out already, although none of that makes any sense with modern technology.

First of all, a lifting body or spaceplane makes no sense for a multi-purpose exploration lander. By definition, you are exploring, so you don't really know what kind of atmosphere (or lack of) you will encounter. A space plane or lifting body would be pointless if the planet has an atmospheric density or composition that is different than Earth.

You would be better off with propulsive landing and takeoff. You could add some sort of aerobraking device (parachute, ballute, inflatable heatshield) to save some fuel when you can, but you will still need enough dV to do a fully propulsive braking and takeoff if you have zero atmosphere.

Now, to takeoff from Earth, you need 9000m/s of dV. With a multistage rocket, and a 100ton payload, this takes a serious heavy lifter such as the Saturn V or SLS. If you wanted the Saturn V to be an SSTO, it would have to be twice as big. But if you wanted it to takeoff AND land propulsively without aerobraking, it would need 18000m/s of dV, meaning that an SSTO version would have to be probably 4 times the size of a Saturn V.

You talk about NERVA, but that isn't much of a high-thrust engine for leaving the ground. It was a low-thrust high ISP space-only engine. However, high ISP doesn't make it a miracle engine. That means that it needs less propellant. Something like half less. So using a magical high thrust NERVA engine with a magical nozzle that works efficiently at all altitudes, your 18000m/s dV SSTO rocket still needs to be twice the size of a Saturn V.

So the whole idea is ludicrous. If you have magical warp engines that can send you to another star, then why bother with boring chemical propulsion for your shuttle.

[PB666]

I'm not sure what kind of input you are expecting from this thread. You seem to have it all figured out already, although none of that makes any sense with modern technology.

He thinks he's got it figured out. Anyway let's not step on his dream to quickly

First of all, a lifting body or spaceplane makes no sense for a multi-purpose exploration lander. By definition, you are exploring, so you don't really know what kind of atmosphere (or lack of) you will encounter. A space plane or lifting body would be pointless if the planet has an atmospheric density or composition that is different than Earth.

Right, but his problem is exactly worse than that . . . . . . .

You would be better off with propulsive landing and takeoff. You could add some sort of aerobraking device (parachute, ballute, inflatable heatshield) to save some fuel when you can, but you will still need enough dV to do a fully propulsive braking and takeoff if you have zero atmosphere.

Now, to takeoff from Earth, you need 9000m/s of dV. With a multistage rocket, and a 100ton payload, this takes a serious heavy lifter such as the Saturn V or SLS. If you wanted the Saturn V to be an SSTO, it would have to be twice as big. But if you wanted it to takeoff AND land propulsively without aerobraking, it would need 18000m/s of dV, meaning that an SSTO version would have to be probably 4 times the size of a Saturn V.

Imagine you had an engine that could take you from Sol to system X, are we doing this for minerals, nope that would be silly, are we doing it to explore, nope we can do that with much cheaper space telescopes. The reason we are doing this is to assess planets as expansion points.

You talk about NERVA, but that isn't much of a high-thrust engine for leaving the ground. It was a low-thrust high ISP space-only engine. However, high ISP doesn't make it a miracle engine. That means that it needs less propellant. Something like half less. So using a magical high thrust NERVA engine with a magical nozzle that works efficiently at all altitudes, your 18000m/s dV SSTO rocket still needs to be twice the size of a Saturn V.

So the whole idea is ludicrous. If you have magical warp engines that can send you to another star, then why bother with boring chemical propulsion for your shuttle.

[Rune]

Actually, I think I have the kind of feedback you are looking for: your SSTO is much too overcomplicated. Also, impossible. And it is not a SSTO if it has more than one stage, that too, and yours sheds a lot of stuff.

First, you can't have a NERVA-like reactor running on Hydrogen running on anything else. The cooling channels on the reactor are designed with hydrogen's density in mind, so they won't work for anything else. Or, the Pluto-like engines won't work with hydrogen, one of both.

Thankfully, there is already a nuclear engine design specifically thought as a SSTO: DC-X. NERVA-like engines can give you TWR over one with delta-v's over 10km/s if they are properly designed, and then the only other thing you need is landing gear strong enough to support it. Though considering how hot the tail would be after a powered landing on the main engines, maybe auxiliary chemical landing engines would be preferable.

And then there's the QED ARC Polywell fusion engines. Those are much more theoretical, since no one even knows if a polywell even works, but if you believe that very speculative paper, then, well... fusion SSTO spaceplanes with near-future tech! That looks positively sci-fi.

Rune. Being a pebble bed, the core on a nuclear DC-X can also be safely dumped to space after the main burn, that's another plus.

Edited March 7, 2015 by Rune

[EzinX]

I'm not sure what kind of input you are expecting from this thread. You seem to have it all figured out already, although none of that makes any sense with modern technology.

First of all, a lifting body or spaceplane makes no sense for a multi-purpose exploration lander. By definition, you are exploring, so you don't really know what kind of atmosphere (or lack of) you will encounter. A space plane or lifting body would be pointless if the planet has an atmospheric density or composition that is different than Earth.

You would be better off with propulsive landing and takeoff. You could add some sort of aerobraking device (parachute, ballute, inflatable heatshield) to save some fuel when you can, but you will still need enough dV to do a fully propulsive braking and takeoff if you have zero atmosphere.

You talk about NERVA, but that isn't much of a high-thrust engine for leaving the ground. It was a low-thrust high ISP space-only engine. However, high ISP doesn't make it a miracle engine. That means that it needs less propellant. Something like half less. So using a magical high thrust NERVA engine with a magical nozzle that works efficiently at all altitudes, your 18000m/s dV SSTO rocket still needs to be twice the size of a Saturn V.

So the whole idea is ludicrous. If you have magical warp engines that can send you to another star, then why bother with boring chemical propulsion for your shuttle.

Maybe you built the descent vehicle after you already arrived, or sent a probe earlier. So you know the parameters of the landing environment.

NERVA is a high thrust engine. Saturn V upper stage. And reaching Mach 4 at sea level. And, presumably, you can optimize the design a bit since the 1960s designs.

And I specifically said to just take it as granted you have warp drive but nothing else. Please stop pooping on my thread. If it helps make the problem easier to see, let me rephrase it. Space aliens have opened a magic portal located in geosynchronous orbit over an earth like planet. How to get down and then back up again? You have only tech we have right now, or can develop from known prototypes.

If it's impossible, just say so.

[Armchair Rocket Scientist]

Now, to takeoff from Earth, you need 9000m/s of dV. With a multistage rocket, and a 100ton payload, this takes a serious heavy lifter such as the Saturn V or SLS. If you wanted the Saturn V to be an SSTO, it would have to be twice as big. But if you wanted it to takeoff AND land propulsively without aerobraking, it would need 18000m/s of dV, meaning that an SSTO version would have to be probably 4 times the size of a Saturn V.

You talk about NERVA, but that isn't much of a high-thrust engine for leaving the ground. It was a low-thrust high ISP space-only engine. However, high ISP doesn't make it a miracle engine. That means that it needs less propellant. Something like half less. So using a magical high thrust NERVA engine with a magical nozzle that works efficiently at all altitudes, your 18000m/s dV SSTO rocket still needs to be twice the size of a Saturn V.

You're calculating required vehicle masses linearly, when due to the nature of the rocket equation it's actually exponential:

dV = g * isp * ln(wet mass / dry mass)

wet mass / dry mass = e^(dv/g/isp)

mass ratio = e^(dv/g/isp)

So: mass ratio = (payload mass + fueled mass of rocket) / (payload mass + dry mass of rocket) = e^(dv/g/isp)

Now, for a dV of 9000 m/s (by the way, this only BARELY gets you into orbit with nothing left for deorbit or orbital adjustment) and an isp of 450 (chemical fuel with hydrogen), the required mass ratio is about 7.68. For a more reasonable dV of 9.5 km/s, it's 8.60. Now, to get our payload fraction, we need to subtract the structural mass of the vehicle from the dry mass. Let's assume the structural mass is 5% of the fueled mass - this is comparable to a F9R first stage, and it uses kerosene fuel (high density + non-cryogenic = good tank mass fractions) and the highest TWR liquid-fueled engines ever flown, so this is VERY optimistic.

So: (payload mass + fueled mass) / (payload mass + 0.05 * fueled mass) = 8.60.

payload mass + fueled mass = 8.60 * payload mass + 0.430 * fueled mass

7.60 * payload mass = 0.570 * fueled mass

fueled mass = 13.33 * payload mass.

launch mass = 14.33 * payload mass, or 1433 tons for a 100 ton payload. This is much lighter than a Saturn V, but we used an unrealistic mass fraction for our rocket: it's more realistic to assume dry mass is around 10% of fueled mass for a cryogenic stage. This gives us a launch mass of about 5400 tons, which is close to double a fully fueled Saturn V (and the Saturn's payload is a bit more than 100 tons actually).

Anyway, now let's switch out our hydrolox engines for a solid-core NTR with an isp of 900 s, and keep the mass fraction the same.

With our higher isp, we get:

(payload mass + fueled mass) / (payload mass + 0.10 * fueled mass) = 2.93.

Our launch mass ends up being 373 tons for a 100 ton payload. Holy mackerel! Doubling our specific impulse didn't half our launch mass, it cut it by more than ten times! Unfortunately, our actual mass ratio won't be that high, since (a) nuclear engines and their associated shielding are heavy ( the vehicle needs to survive reentry for safety reasons, and © again for safety reasons we'll want fairly high structural safety margins.

Now, let's look at a rocket with a dV of 19,000 m/s (enough to make a propulsive landing on an Earthlike planet with no atmosphere and launch back into orbit).

With hydrolox engines, our launch mass must be e^(19000 / 9.81 / 450) = 74 * (dry mass of rocket + payload mass).

Oops. Even the lightest rocket stage we've ever built, launched with no payload at all, is still three times too heavy. Let's try again with NTRs.

(payload mass + fueled mass) / (payload mass + dry mass) = e^(19000/9.81/900) = 8.6 (hey, this number looks familiar).

Turns out our nuclear rocket with a dV of 19 km/s DOES end up being about twice the size of a Saturn V, but a chemical-fueled one turns out to be utterly impossible.

Fortunately for OP, if we can build a warp drive we can probably build a closed-cycle gas-core NTR (aka a "nuclear lightbulb"), which would have an ISP of at least 1500. Or, better yet, we could use some type of fusion reactor. For that matter, less than a gram of the antimatter used for the mothership will provide plenty of energy to reach orbit provided we can find some way of using it to make a jet or rocket engine usable in atmo.

Also, if we're exploring the stars with a ship like this, it's reasonable to assume we're looking for potential colonization sites. If a planet has so little atmosphere that we can't aerobrake or run a nuclear-thermal jet engine (Mar's atmosphere makes both difficult but possible), then just leave and find another target, and send a small robotic lander to do some basic measurements on the feasibility of terraforming the place.

[Bill Phil]

Maybe you built the descent vehicle after you already arrived, or sent a probe earlier. So you know the parameters of the landing environment.

NERVA is a high thrust engine. Saturn V upper stage. And reaching Mach 4 at sea level. And, presumably, you can optimize the design a bit since the 1960s designs.

And I specifically said to just take it as granted you have warp drive but nothing else. Please stop pooping on my thread. If it helps make the problem easier to see, let me rephrase it. Space aliens have opened a magic portal located in geosynchronous orbit over an earth like planet. How to get down and then back up again? You have only tech we have right now, or can develop from known prototypes.

If it's impossible, just say so.

Just use a multistage vehicle. No NERVA needed at all.

[Majorjim!]

As the op stated, this scenario assumes 'warp' drive exists.

I say we could just as easily say the technology can be miniaturised too and used on a lander as a form of 'anti gravity'.

Seeing as a warp drives essentially does what gravity is, ie, a compression of space-time.

With this drive the lander could simply, rise up from the planet.

Edited March 7, 2015 by Majorjim

[PB666]

As the op stated, this scenario assumes 'warp' drive exists.

I say we could just as easily say the technology can be miniaturised too and used on a lander as a form of 'anti gravity'.

Seeing as a warp drives essentially does what gravity is, ie, a compression of space-time.

With this drive the lander could simply, rise up from the planet.

Or make the planet move 2000km to the right then spool up the warp drive. The infinite improbability drive, made everyones underwear moved 3 feet to the right, got the physics engineers party going.

If we live in a fantasy land, you warp to within 100 ft of the planets surface Parachute to a landing with thrusters, open up a worm hole and walk back, cause who really needs physics engineers having a party, anyway.

[Exoscientist]

Don't know if these can both takeoff and land on a single fueling but links to some proposals for a nuclear SSTO are here:

http://nextbigfuture.com/2009/06/nuclear-dc-x-recent-nuclear-thermal.html

BTW, I don't agree that a chemical propulsion SSTO isn't feasible. First, find out what's the highest ISP for a first stage kerosene engine, i.e, one that can operate at sea level, not an upper stage engine. Then find out what kerosene first stage has the highest mass ratio.(Hint: it's by a six letter launch company). Next use the rocket equation to calculate what would be the delta-v if you married this highest ISP efficiency engine with this highest mass efficiency stage. Note the answer is well above the delta-v needed to get to LEO.

Bob Clark

Edited March 7, 2015 by Exoscientist

[Nibb31]

Chemical SSTO is certainly possible if you have a throttlable engine high-thrust engine. It's chemical SSTO with re-entry landing systems and a usable payload that is pretty much impossible.

I still think that if you are stuck on using SSTO, then VTVL (rocket+tankage+payload) is more efficient than a spaceplace (rocket+tankage+payload+wings+hydraulics+landing gear). Horizontal landing requires xtra hardware that necessary eats into your payload.

[EzinX]

Ok. What I'm starting to see here is a dual-fuel rocket with a linear aerospike engine. It's sorta long and skinny, but not really. It's inside a heat shield.

After the hot part of reentry is over, you deploy a parachute and also eject the heat shield. You're still going really fast - this thing isn't very aerodynamic. It's basically just a long tank with some landing legs at the bottom and the aerospike engine is down there. You do a powered landing. Once on the ground, you have a small nuclear reactor or solar panels, whichever is more mass efficient. You refuel the fuel tanks with liquid methane and liquid hydrogen - that's why it's a dual fuel engine.

When it's time to liftoff, you leave behind your base camp payload, your landing legs, basically everything but a small capsule at the top with the crew. Dual fuel makes the fuel tanks for the first part of the flight lighter (liquid methane has better density and can be stored in a lighter tank)

You barely make orbit. Mothership picks you up. You only need to replace the heat shield, the landing legs, and some propellant for the next landing.

If you were god's gift to engineering and confident you could actually do your next landing on engine thrust right into a cradle supported by the original landing legs. Then you only need some propellant and a heat shield per additional mission. You don't throw fuel tanks away, and you don't have the problems with radiation caused by using nuclear thermal.

If you had futuristic supermaterials (like nanostructured carbon or something) you wouldn't need a heat shield. Your fuel tank walls, light enough for SSTO, would also be able to tolerate the heat and pressure of reentry. Once back at the base camp, robots would repair nanoscale damage for the next run.

Then you just need to add some propellant to your tanks, taken from the mother ship's stores, every time you do another shuttle trip, in order to do the powered landing.

Yes, this is a drastically better idea than mine. Also works on vacuum worlds just fine.

Edited March 8, 2015 by EzinX

[EzinX]

So how do we get more fuel for our spacecraft? That's where NERVA comes in. We need a vehicle that can skim the atmosphere of a planet, flying at scramjet speeds and refueling it's own tanks enough to extra net propellant.

I think just a lifting body rocket/scramjet could be done. It doesn't have to fly slower than about half of orbital velocity, and it only has 2 modes of flight : scramjet, and rocket.

Instead of trying to make a reactor able to handle 2 kinds of propellant, you would actually move the reactor core (the heavy part) from one part of the reactor to another, in flight. The whole fuel rods would be pushed down or some simple mechanism like that. So you'd have your hydrogen rocket plumbing, and your scramjet plumbing, and each is made of a different material and has different sized tubes.

[Rune]

Ok. What I'm starting to see here is a dual-fuel rocket with a linear aerospike engine. It's sorta long and skinny, but not really. It's inside a heat shield.

After the hot part of reentry is over, you deploy a parachute and also eject the heat shield. You're still going really fast - this thing isn't very aerodynamic. It's basically just a long tank with some landing legs at the bottom and the aerospike engine is down there. You do a powered landing. Once on the ground, you have a small nuclear reactor or solar panels, whichever is more mass efficient. You refuel the fuel tanks with liquid methane and liquid hydrogen - that's why it's a dual fuel engine.

When it's time to liftoff, you leave behind your base camp payload, your landing legs, basically everything but a small capsule at the top with the crew. Dual fuel makes the fuel tanks for the first part of the flight lighter (liquid methane has better density and can be stored in a lighter tank)

You barely make orbit. Mothership picks you up. You only need to replace the heat shield, the landing legs, and some propellant for the next landing.

If you were god's gift to engineering and confident you could actually do your next landing on engine thrust right into a cradle supported by the original landing legs. Then you only need some propellant and a heat shield per additional mission. You don't throw fuel tanks away, and you don't have the problems with radiation caused by using nuclear thermal.

If you had futuristic supermaterials (like nanostructured carbon or something) you wouldn't need a heat shield. Your fuel tank walls, light enough for SSTO, would also be able to tolerate the heat and pressure of reentry. Once back at the base camp, robots would repair nanoscale damage for the next run.

Then you just need to add some propellant to your tanks, taken from the mother ship's stores, every time you do another shuttle trip, in order to do the powered landing.

Yes, this is a drastically better idea than mine. Also works on vacuum worlds just fine.

You are asking a lot of chemical propulsion, even for a tripropellant engine. The russkies didn't think they could make that work, not without an air launch assist and an expendable external tank. Going nuclear with a higher isp would give you some mass fraction breathing room to stick the heatshield and ISRU equipment in.

And I say heatshield and ISRU equipment, because you can't make do without those. The equivalent energy to the ground-to-orbit burn has to be dissipated in order for you to stop, so if you don't make it go with the heatshield as it ablates, or with a retro burn, you have to sink it into the airframe and re-radiate, so you quickly start glowing white. Especially if you land of full tanks! Then your ballistic coefficient would be crap and stopping it before the ground wold be incredibly difficult, needing massive heatshields and landing systems. Now, if you land it empty, that is much less mass to stop, so much less energy to shed. Plus, much less thrust to land propulsively, so you don't need to light the main engine, auxiliary chemical rockets wouldn't be such a mass hit and would save you the deep throttling and multiple firings requirement on the main propulsion system.

And if you are worried about nuclear engines becoming hot after a firing, as I said, with pebble bed systems you can dump the whole radioactive core away in orbit and put new fresh fuel afterwards. Another reason for auxiliary landing systems, that way the nuclear engine can land "cold".

Chemical-only SSTOs probably won't have good enough payload fraction to be useful, if you add the reentry requirement, sorry. Even doing clever things like Skylon to use atmosphere as extra reaction mass on the way up won't yield mass fractions that allow for the big payload margin that ensures a robust design.

Rune. Especially if it has to operate without ground support systems!

[dryer_lint]

Are we allowed to use Rangers?

Because phyzicz.

[Bill Phil]

How about just probes? Except for sufficiently low gravity bodies, like the moon.

[EzinX]

. Now, if you land it empty, that is much less mass to stop, so much less energy to shed.

Of course I meant land empty. The first landing, you've got 10% or so (don't know the exact amount but it's a small fraction of the max fuel load) full tanks, and your vehicle is loaded down with cargo for doing ISRU, setting up the base camp, etc. Even though your vehicle is moderately heavy for it's size, you deploy parachutes (that's how you get heat shield separation) and you do a propulsive landing to go from your terminal velocity (couple hundred m/s maybe) to zero.

You fill up to completely full tanks on the ground, and leave absolutely everything behind. You only make orbit, barely, with an empty set of fuel tanks, your 1 big engine, and a tiny capsule at the top shaved to the gram.

Then, for the next trip, the mothership gives you just enough fuel to make a suicide burn into the docking cradle (the docking cradle would be the deployed lander legs and some supporting structure you left behind) and just enough heat shielding to not burn up on the way down.

As a side note, during reentries, you have your fuel tanks under pressure so the outside pressure doesn't collapse them. You might run the engines and inject hot gas back into the fuel tanks as the pressure on them increases.

[Nibb31]

If you're exploring a planet around another star, you shouldn't count on ISRU to refuel because you don't know what you're going to find. If you want a multi-role exploration shuttle (Like the Ranger from Interstellar) this is not going to work. You need to land with the propellant to bring you back, Apollo-style.

If you're assuming that your destination planet is exactly like Earth, then what you're asking for is the same as any Earth-bound launcher (refuel-launch-land empty). Also, my little finger tells me that scooping air at hypersonic speed to make more fuel than what you are spending to scoop the air at hypersonic speed isn't going to work. If it did, we would already be doing it.

Then, you also seem to want SSTO, but you insist on dropping stuff. Sorry, but as soon as you drop something, you are no longer single-stage. And what's the point of claiming to be single-stage at all in that case? If you're leaving legs and heatshields on the surface, you might as well just go full Apollo with a two-stage lander. It makes things much simpler.

[EzinX]

If you're exploring a planet around another star, you shouldn't count on ISRU to refuel because you don't know what you're going to find. If you want a multi-role exploration shuttle (Like the Ranger from Interstellar) this is not going to work. You need to land with the propellant to bring you back, Apollo-style.

If you're assuming that your destination planet is exactly like Earth, then what you're asking for is the same as any Earth-bound launcher (refuel-launch-land empty). Also, my little finger tells me that scooping air at hypersonic speed to make more fuel than what you are spending to scoop the air at hypersonic speed isn't going to work. If it did, we would already be doing it.

Then, you also seem to want SSTO, but you insist on dropping stuff. Sorry, but as soon as you drop something, you are no longer single-stage. And what's the point of claiming to be single-stage at all in that case? If you're leaving legs and heatshields on the surface, you might as well just go full Apollo with a two-stage lander. It makes things much simpler.

This is debatable. What you are dropping is presumably relatively smaller and light. Heat shield plates would be thin plates of some kind of wonder ceramic-carbon-composite whatsit that can tolerate the heat. And, you only drop the plate protecting your engines in flight. The plates protecting your fuel tanks you would drop before launching again. (you'd use em to make shacks to live in or something on the ground). Or, with future materials, you might be able to make your fuel tanks and engines heat resistant enough that this isn't even needed (and the tanks and engines would still be light enough for SSTO)

The main thing is that if it's partial SSTO, you might be able to do 10 or 20 launches and landings with a single shuttle for the same total mass carried on the mothership as 2-3 landers that can only do one trip each.

Your point is received regarding ISRU. You can't rely on finding hydrogen and carbon just anywhere.

Regarding scooping gas : the way this is possible uses a nuclear engine that has insane performance (multiple gigawatts of output power) and it will leak fission fragments in the exhaust. That's why you gain net fuel this way, because the engine sustains your speed during the hypersonic flight, and it does the burns to put you back into orbit at a very high ISP.

Now I'm wondering what other options there are to get the needed performance. Perhaps ablative laser propulsion? (the mothership would carry a very large laser onboard). It would vaporize a chunk off the lander vehicle to give it net thrust with an ISP of better than 2000. (and high thrust as well). And ablative laser propulsion propellant is solid blocks of homogeneous material - you could probably make it from a large variety of possible elements found on other planets.

Problems include the fact that your laser mirror has to be gigantic to get a decent spot size. If the mothership is in geosync, it has to focus precisely on specific spots on your ascent vehicle from 35k meters away, at the correct angle...probably be easier to set up a mirror on the ground that acts as a relay and beam combiner.

Edited March 8, 2015 by EzinX

[Nibb31]

You're talking about crazy magical propulsion methods, yet you insist on jettisonning parts that quite easy to reuse even with current technology: heat shields, landing legs, and molten reactor cores. Why do you want SSTO in the first place?

The main thing is that if it's partial SSTO, you might be able to do 10 or 20 launches and landings with a single shuttle for the same total mass carried on the mothership as 2-3 landers that can only do one trip each.

There is no such thing as partial SSTO. You are either SSTO or MSTO. SSTO is just a pointless label. The number of stages is irrelevant. What is relevant is the mission requirements.

We are perfectly capable of making an SSTO rocket today with current technology. Mercury-Atlas was already "partial SSTO" by your standards, as it reached orbit by just dropping it's booster engines. The Titan first stage would also have been capable of SSTO, if only it had throttlable engines and carried a pointlessly small payload. We could do much better today with modern materials and throttlable engines.

And if we had magical warp drive, no doubt we would also have magical materials that would allow more efficient chemical engines and lighter structures that would make SSTO viable.

The reason we don't do SSTO is because the payload mass fraction is so low so it doesn't make economical sense, not because it's impossible.

Problems include the fact that your laser mirror has to be gigantic to get a decent spot size. If the mothership is in geosync, it has to focus precisely on specific spots on your ascent vehicle from 35k meters away, at the correct angle...probably be easier to set up a mirror on the ground that acts as a relay and beam combiner.

You're trying to find complicated answers to easy questions. In a hypothetical future with hypothetical warp drives, you can have any sort of hypothetical shuttle with another hypothetical propulsion system. In the OP you claimed you wanted current or near-future technology, yet you are suggesting science-fiction technobabble. Ablative laser propulsion or insane nuclear engines are just as hypothetical as the warp drive that you are starting with.

Edited March 8, 2015 by Nibb31

[EzinX]

You're trying to find complicated answers to easy questions. In a hypothetical future with hypothetical warp drives, you can have any sort of hypothetical shuttle with another hypothetical propulsion system. In the OP you claimed you wanted current or near-future technology, yet you are suggesting science-fiction technobabble. Ablative laser propulsion or insane nuclear engines are just as hypothetical as the warp drive that you are starting with.

No, they aren't. The nuclear engines already exist and have been tested. (so what if they were only car sized prototypes that never flew, they still worked)

Ablative laser propulsion also exists, and the technology to make lasers big enough now exists as well.

Warp drive doesn't exist. No one has ever demonstrated a warp field at any measurable level. Don't mistake fantasy for straightforward extrapolation of modern engineering. The only reason I had to bring the concept of a "warp drive" into this discussion at all is to bring up the idea of how you might explore another Earth if you could get there in the first place.

[Kryten]

No, they aren't. The nuclear engines already exist and have been tested. (so what if they were only car sized prototypes that never flew, they still worked)

PLUTO was tested. NERVA was tested. A hybrid of the two would be a major, major step beyond either in terms of systems engineering.