How to design a fully reusable multi-stage launch vehicle

[Armchair Rocket Scientist]

So, there are currently attempts to make the first stages of launch vehicles reusable. I know reusability on the Falcon 9's second stage has been shelved in favor of development of the MCT, and nobody else is even considering it.

But let's say I was given the task of designing a fully reusable (aside from a few minor components like payload fairings) launcher.

We'll assume the design is a multi-stage rocket, capable of lifting at least 10 metric tons into LEO - enough for a manned spacecraft, a space station resupply, and some GSO, Molniya, or other high-energy satellite launches. The basic design will be 2STO - the second stage of a 3STO design would have a very high burnout velocity, leaving it on a very difficult reentry trajectory. Strap-on boosters may be used to boost payload capacity as high as 20 tons to LEO. The upper stage will only deliver its payload to trajectories of similar energy to GTO - this is because a reusable stage will naturally have a poor mass ratio making it inneficient to send payloads directly to high-energy orbits, and you're throwing away a reusable vehicle if you put out on an Earth escape trajectory. Some type of "kick stage" will be used for high-energy orbits; this may be a cheap hypergolic or solid-fueled stage, or a pricier cryogenic stage where maximum performance is required.

Choice of fuels: First of all, hypergolics shouldn't be fueling the main engines of a launch vehicle, because they're toxic, corrosive, and otherwise a pain in the ass to deal with. Kerosene's low specific impulse makes it decidedly suboptimal for upper stages. Hydrolox is very efficient, but a bad choice for lower stages because hydrolox engines have a poor TWR and atmospheric ISP. For upper stages, it may not be the best option either due to boiloff. Methane may offer the best of both worlds, offering reasonable density and insulation requirements (boosting mass ratio compared to hydrolox) as well as decent specific impulse and TWR. In addition, it reduces residue in engines compared to kerosene, making reuse easier, and as a gaseous fuel any leaks or spills are inherently less hazardous. Therefore it will be assumed that both stages will use metholox engines.

Stage Recovery:

So, I consider there to be four main ways of landing a stage. 1: parachutes (highest vertical speed on touchdown, very poor accuracy, but easy redundancy by using a cluster of parachutes. 2: parafoils (low vertical speed, some horizontal speed on touchdown. Slight cross-range capability, hopefully allowing a runway to be targeted. Any long skinny object like a rocket would have to land on its side, making landing gear design and parafoil suspension a bit interesting. Harder to make redundant.) 3: wings (effectively zero vertical speed on landing, but very high horizontal speed. Wings are very heavy and add a lot of drag during ascent, but offer excellent cross-range capability). 4: propulsive landing (effectively zero vertical speed and horizontal on landing. Weight penalty is that of reserve fuel, not of engines, and is fairly small. In theory adds little mechanical complexity, but as the Falcon 9 has shown additional control systems may need to be added).

There are also three main places to land a stage: A: On land (this is the best option for an upper stages, but for lower stages this requires lots of dV for a turnaround manuever) B: In the ocean (requires the least dV and landing precision, but saltwater exposure vastly increases maintenance costs, especially for liquid-fueled stages). C: On a floating platform in the ocean (less dV for lower stages. Precision requirements similar to land, but platform drift and wave action make life much harder. Use of a semi-submersible platform instead of a barge like SpaceX has could make things easier).

This gives us twelve options. We can immediately eliminate parachute landing for liquid fueled stages, because the touchdown speeds are unsurvivable for a high mass-ratio stage. An SRB should be okay as long as it lands in the ocean. Winged landing in the ocean is a near-guaranteed crash, and winged landing on a floating platform is unfeasible due to the runway length required. We'll also eliminate water landings of any sort for liquid-fueled stages because they make refurbishment a massive pain. Finally, a winged upper stage would interfere with the vehicle's aerodynamic stability on launch, and is therefore undesirable. This leaves us with:

For upper stage: parafoil or propulsive landing on land.

For lower stage: propulsive or parafoil landing on land (with boostback), winged landing on land (with flyback), or propulsive or parafoil landing on a floating platform.

For boosters: same as lower stage if liquid-fueled. If solid-fueled, glideback and winged touchdown on land, or parachute landing in the ocean.

Now, the velocity of the lower stage and boosters will be kept low enough for a tailfirst reentry, but the second stage will be coming back from orbit, and can't just reenter on its engines. So, it needs a heat shield. With a monolithic heat shield, reentry must be nose-first, but what about with inflatables? Can an inflatable heat shield be designed that will cover the engines, and then be deflated in flight to allow for propulsive landing? For a nose-first reentry, how do you turn the stage around for a propulsive landing? Or is it better to just have special landing thrusters for an "upside-down touchdown?"

For a launch to LEO, the upper stage must have a minimum orbital operation time of 12 hours (enough for the launch site to come below the orbital plane), but 24 hours is preferable to allow for multiple landing opportunities. For a launch to GTO, the stage must perform a small apogee manuever, aerobrake from GTO into LEO 10.5 hours after the initial GTO insertion, boost its periapse, and wait several more hours before deorbiting, again requiring at least 24 hours of on-orbit operations. Is it best to stay simple and use batteries, or are solar panels worth the weight savings? For that matter, since methane will have a little boiloff, what about siphoning off the gases to power a fuel cell or internal combustion engine (Apparently ULA's Vulcan is supposed to power its upper stage this way).

Are there any other ideas you guys have?

[Kibble]

In an upper stage, every kilogram spent on a heat shield, batteries, avionics, and fuel for deorbit and propulsive landing subtracts directly from the payload mass. And for what? Recovering Falcon 9's second stage means you get a small, used fuel tank and one out of the ten rocket engines. Plus all the hardware strapped on to facilitate recovery.

[Yru0]

In an upper stage, every kilogram spent on a heat shield, batteries, avionics, and fuel for deorbit and propulsive landing subtracts directly from the payload mass. And for what? Recovering Falcon 9's second stage means you get a small, used fuel tank and one out of the ten rocket engines. Plus all the hardware strapped on to facilitate recovery.

I think it's an interesting little thought experiment. Doesn't matter whether it'd necessarily be worth doing, but if you HAD to reuse the upper stage - how'd you do it?

I can't really contribute myself, but how do these inflatable heat shields work? I first heard about them with the Vulcan but I can't for the life of me figure out how something inflatable could survive those conditions.

[Acemcbean]

In all honesty, why would you want to recover ALL of it? The most vital parts are the engines, which, if separated correctly, could easily be returned. The tricky part would be returning some upper stage/interstage back to earth as we have this thing called an "atmosphere," and its a pretty darn thick one compared to the other terrestrial planets (,except that dirty peasant planet, Venus! Grrrr...). So basically, we would have to slap on some heat-shielding (which I cant even begin to imagine having to fit somewhere), some parachutes (most likely), and somewhere to land them where we wont be crushing someones hydrangeas. In all honesty, the only components worth getting would be the first stage (because those are probably the biggest, most expensive engines) and some of the more specialized, expensive engines. Even then, all this is a bit too expensive for what its worth.

[Mr Shifty]

Finally, a winged upper stage would interfere with the vehicle's aerodynamic stability on launch, and is therefore undesirable.

You've just eliminated the Space Shuttle Orbiter.

[magnemoe]

In an upper stage, every kilogram spent on a heat shield, batteries, avionics, and fuel for deorbit and propulsive landing subtracts directly from the payload mass. And for what? Recovering Falcon 9's second stage means you get a small, used fuel tank and one out of the ten rocket engines. Plus all the hardware strapped on to facilitate recovery.

You would like to save the upper stage, guess cost is 1/5 to 1/8 of first stage.

SpaceX at least had an plan of returning upper stage, heatshield in front and flip around before landing.

Another idea would be to have an lifting body upper stage, this would let you land on side, think an larger dream chaser. This however would be more suitable for an manned stage.

One idea would be to just return engine and flight control system. same as ULA plans for first stage however this would be an less than 2 ton package.

Lifting body with drop tank like the shuttle on top of an falcon 9 style lower stage should also work.

[Rakaydos]

...What about a design where a winged second stage doubes the wing as a hardpoint location for strap on boosters?

The strapons do a spaceX return to the launchsite, after geting the winged second stage above most of the atmmosphere with some horizontal veocity; the secondstage is a flyback booster, after getting the third stage mostly to orbit; the third stage achieves stable orbit, then plans a targetted reentry.

[Frybert]

You've just eliminated the Space Shuttle Orbiter.

Hence why we're back to capsules.

[Frozen_Heart]

I would say SpaceX is pretty damn close. Differences I would have are:

- Methane fuel. Has a better ISP than Kerosene while not being an utter pain to handle like Hydrogen

- larger than the Falcon 9. The Falcon 9 is restricted in size due to being transported by road. Without this restriction Methane is a viable fuel and so the vehicle could afford second stage reusability like was originally planned for the F9.

[Mr Shifty]

Hence why we're back to capsules.

I'm not saying winged upper stages are the way to go, but categorically excluding them from speculation here is baseless.

[AngelLestat]

There are so many possibilities for a reusable launch vehicle, all are valid methods, very hard to choose the perfect balance.

The vehicle with our current technology may be 2 stage or 3stage to orbit.

The most difficult to solve is the second stage reusability in a 3stage vehicle. And that makes me wonder... what are the benefics of a 3 stage vehicle against 2 stage?

If the second stage already puts things into orbit, after that you only need to decelerate a bit and fall.

Also vehicles with low density due size reduce the amount of thermal shielding needed.

I will thoght in one possibility maybe inspire by the falcon9.

Things that I have for sure... the first stage would use rotor-blades with autorotation instead rockets+fins to land. I will choose methane for the first stage and hydrogen ballon tank for the second.

I cant think in a good idea to recover the second stage.. I would see.

In case the payload is big enoght to not be able to go back to base, I would use a manned barge to that task.

[Armchair Rocket Scientist]

You've just eliminated the Space Shuttle Orbiter.

Well, this vehicle would hopefully be capable of launching a variety of payloads, including manned spacecraft. Putting something manned in the cargo bay of a normally unmanned orbiter would be a death trap, but as the space shuttle has proven launching crew and cargo on the same vehicle means you're not using your full capability on most missions. So, you need separate manned and cargo upper stages, somewhat like this. But having a manned vehicle sitting on the side of your stack is a death-trap anyway, as demonstrated again by the Space Shuttle.

So you basically have to have an inline upper stage, as Magnemoe suggests:

Another idea would be to have an lifting body upper stage, this would let you land on side, think an larger dream chaser. This however would be more suitable for an manned stage.

The main problem I see with this is: where do you put the payload? In a cargo bay? (If so, the fully-fueled second stage has to be capable of acting as an LES in the event of a lower-stage failure, which will require a stronger structure and HUGE engines). If it's on the front, then once the payload is jettisoned the nose of the vehicle would probably be pretty much flat, which isn't that good for reentry.

Perhaps a side-mounted inflatable heat shield with a lifting body shape?

Lifting body with drop tank like the shuttle on top of an falcon 9 style lower stage should also work.

Like this? It might work, but it still has a lot of the problems of a purely side-mounted upper stage, including LES capability and the heat shield being potentially exposed to falling debris from the fuel tank.

...What about a design where a winged second stage doubes the wing as a hardpoint location for strap on boosters?

That might put a lot of stress on the wing structure, but using the second stage fuel tank as a hardpoint might work better, as long as the payload fairing / capsule is located safely above the tops of the boosters.

The strapons do a spaceX return to the launchsite, after geting the winged second stage above most of the atmmosphere with some horizontal veocity; the secondstage is a flyback booster, after getting the third stage mostly to orbit; the third stage achieves stable orbit, then plans a targetted reentry.

From what I know, "mostly to orbit" isn't a great situation to reenter from. If you look at a chart of the Shuttle's abort possibilities here,, there are big "black zones" late in the mission. With a lifting body the g-loads might be reducable to safe levels, but flyback would take an absurd amount of fuel. A better option would probably be landing on another continent, possibly with some "boost-forward," similar to the Shuttle's TransAtlantic Abort Mode, or even an Abort Once Around. This option would be most effective when launching beyond LEO.

Also, it looks like inflatable heat shields are pretty cool technology: http://www.researchgate.net/publication/238029355_The_ParaShield_entry_vehicle_concept_-_Basic_theory_and_flight_test_development

[Rakaydos]

Yea, I really meant a "fly-foreward" core that lands on another contenent.

After playing around with the idea in sandbox, I've discovered that it's really hard to design a flyback booster without soe kind of noseweight- empty of fuel, the engines are so much heavier than the tanks that your wings look like overly large tailfins.

[magnemoe]

I'm not saying winged upper stages are the way to go, but categorically excluding them from speculation here is baseless.

http://d1jqu7g1y74ds1.cloudfront.net/wp-content/uploads/2013/10/dream-chaser-5.jpg

Agree, one of the benefits of wings is that the huge second stage vacuum engine is protected during reentry.

You also has the option to use a drop tank like the shuttle, as this would be second stage it could be smaller.

[Superluminaut]

Stage Recovery:

So, I consider there to be four main ways of landing a stage. 1: parachutes (highest vertical speed on touchdown, very poor accuracy, but easy redundancy by using a cluster of parachutes. 2: parafoils (low vertical speed, some horizontal speed on touchdown. Slight cross-range capability, hopefully allowing a runway to be targeted. Any long skinny object like a rocket would have to land on its side, making landing gear design and parafoil suspension a bit interesting. Harder to make redundant.) 3: wings (effectively zero vertical speed on landing, but very high horizontal speed. Wings are very heavy and add a lot of drag during ascent, but offer excellent cross-range capability). 4: propulsive landing (effectively zero vertical speed and horizontal on landing. Weight penalty is that of reserve fuel, not of engines, and is fairly small. In theory adds little mechanical complexity, but as the Falcon 9 has shown additional control systems may need to be added).

I think you left out one of the better option. Heli blades. There is a guy on the forums that converted me and knows more about this, but I'll have a go at defending the option.

So you would dive in the the atmosphere, top of the stage going prograde with a heat shield. Once you hit the desired altitude for deploying the heli blades you unlock them from the side of the stage and aerodynamic forces automatically deploy them as well as spin them up. So now you have an upside down fuel tank with a nozzle pointing up slowing down due to the lift provided by the free spinning heli blades. At this point you have control and can fine tune your dive towards the landing pad by angling the blades. You dive in just like a lifting body would and right above the landing pad you set the angle of the heli blades for maximum lift, they spin up and allow you to make a soft, controlled landing, no engine required, just gravity, air, and controlling the angle of the blades. This method also allows for a glide slope so you can guide the vehicle to the pad.

The technique of diving in and allowing the blades to spin up for a soft landing is a proven technique employed by helicopter pilots in the event of an engine malfunction in the air.

5; Rotors (zero vertical and horizontal speed on touchdown, with cross-range capability. Blades require some moving parts similar to falcon 9 control systems, and are a medium weight option.)

[Hummingbird Aerospace]

Maybe for the first stage booster you could remove most of the fins and control systems, but leave on the RCS for precise corrections, and have some drouge chutes at the top to balance the booster onto the retrograde course, and then use a quick burst of the engine(s) to kill of any excess velocity. That way, wou wouldn’t need grid fins and reaction wheels and all that other stuff.

[Xd the great]

The bfr is a good start.

Or, use a falcon heavy boosted space shuttle, with modifications to the ship to use vacuum optimised engines. And use more space for fuel tanks.

[T-10a]

My idea of a reusable TSTO goes as such:

Lower stage:

• Parafoil landing flying back to the launch facilities, preventing the mentioned headaches of water landings. Parafoil chosen due to low relative mass, and ease of removal for use as a disposable first stage (to accelerate flight times, allowing it to fly regardless of the readiness of the recovery). Also, it allows the first stage to fully deplete propellant regardless of recovery factor, as for SpaceX style reuse you MUST sacrifice payload capacity for reuse.
• First-stage engines are hydrolox for greatest specific impulse. Engines are designed to be swapped out quickly for other engines so that complex flight checks can be done without impacting the flight schedule while prepared, ready to go engines are fitted for flight.
• Hybrid boosters are provided due to relative low cost, and utilize LOX from the main tank as the oxidizer. This allows the shutoff and throttling of these motors, in the event of anomalous behavior. These are recovered shuttle-booster style, as the pumps are actually fitted inside the lower stage, allowing more "rough" recovery of motors.

Upper stage

• Upper stage is of the following types:
  • "Disposable" high-energy (ACES or something similar) stage (called HEUS from now on). Face it, not everything is going to be reusable on the ground so why not reuse hardware in space?
  • Recoverable crew lifting body shuttle w/ pushing abort motors, which are jettisoned on a suborbital trajectory alongside the booster.
  • Crew Shuttle-derived Recoverable Vehicle (a special cargo-focused vehicle derived from above-mentioned shuttle, either for use pressurized as a resupply vehicle or unpressurized for satellite recovery or external payloads.
• Upper stages also use LH2/O for greatest ISP as well, alongside being a common propellant for both stages.
• The HEUS is basically ACES, so see that for more details.

What do you guys/gals/pals think of this? 

Edited September 11, 2018 by T-10a

[kerbiloid]

Imho:

A family of rockets using same construction equipment where it's possible.
Not same tanks, but same tank diameters.

36 t to LEO - for daily needs: a 30+ t spaceplane, sat packs, spacestation modules, TKS-like single-use crafts when reusability of spaceplane makes no sense.
The main launch vehicle.

~1500 t - for big things like

• a whole standard interplanetary ship (~500 t dry in my estimation if without boosters),
• same ship with gas-core propulsion module
• a medium-sized standard orbital station (unified with the interplanetary ship),
• a booster stage for chemical interplanetary ship

~150 t - not too much needed, but uses the existing equipment and intermediate diameters from 36 and 1500 ones.
Useful to lift fresh excursion modules to a reusable interplanetary ship (~100 t in my estimation).

Lower stage.

Reusable
With a single aerospike engine, which works as both engine and heatsheild, maybe also even as a well for technical elevator 
Methalox, due to availability in huge amounts and for unification with extraterrestrial modification. Say, to use the reusable 1st stage on Earth as a reusable SSTO on Mars (if use local methane).

Probably (though not necessary) a Saturn/Proton design with a large axial tank surrounded with 6-8 radial ones (all are cylindric).
The cylindric hull of the central one carries the upper stage on top, and it's a truss for the aerospike engine,. 
So, radial tanks don't carry the cargo directly, they are strapped.

Between the radial tanks there are niches,

Inside the niches maybe (not necessary if the hull itself is enough strong) there are 6-8 vertical bars/columns.  
On top the columns and the upper edge of the central tank are covered/connected with a wider ring on which the second stage is put.
Radially these niches (and bars) are the structure to attach landing legs, RCS, etc.

Below the bottom a ring of the same diameter is used to attach the propulsion module (central aerospike + several radial auxilliary engines).
So, like the bars (if any) connect the cargo ring and the engine ring, and the central tank in between enforces them

When used as reusable (so, in most cases) has legs in the niches between the radial tanks, and is covered by a conform lifgtweight shroud envelope, looking biconical.
When working, the aerospike makes the thrust, auxilliary ones are RCSing.
After the second stage separation performs a retrograde horizontal impulse with auxilliary engines (they are much smaller), makes a parabola, maybe retracts the aerospike nozzle, maybe not.
Lands at the launch field, gets delivered to VAB.

In a single-use mode doesn't have legs and shroud.

Looks same (just scaled) for all rockets of the family.

Upper stage.

Doesn't include a spaceship or so, just a pure boosting stage.

Partially reusable. A reusable propulsion module with a single-use tank pack.

Methalox for the 36t rocket (to minimize headache with fuel diversity).
Hydrolox for the 1500 t rocket,

Probably has the same tank-pack design with a central tank and radial tanks.
Can lift either like-the-central-tank wide payloads (say 4 m for 36 t, 25 m for 1500 t), or external-diameter-wide payload (8 m and 48 m correspondingly) on an external ring.

The propulsion module includes everything to be reused: aerospike main engine, auxilliary engines, command block, legs, and so on.
The aerospike bottom plate is a heatshield (mainly that's why aerospike).

After reaching the LEO and detaching the payload, the propulsion module separates from the tank module, performs 1-2 turns, deorbits (with small inner tanks), and lands on the launch field.

The tank module is single-use. It either deorbits and burns, or (better case) gets delivered by a tug to the shipyard orbital station to be disassembled and either reused for further needs, or put into a mill and turns into metal scrap to be stored in a trashcan and maybe later reused.
Also this goes easier as it consists of 9 smaller tanks rather than a single large one,

The same happens with large shrouds if any. No reusable shrouds.

Triple huge.

~5000t to LEO for the hugest single part to be put in LEO in one piece
(a 50m-wide drum with coaxial radially attached counter-rotating habitats with artificial gravity, for a standard heavy space station).

First stage.
Pack of 3 first stages from the 1500t-lifting LV like Falcon Heavy.
Single-use, no legs, no return.

Second stage.
Central module - fuel tank(s) and hydrolox engine.
Two side modules - fuel tank and a gas-core nuke.
Gets to LEO on a single chemical engine (for thrust) and two side nukes (for ISP).
Either both nuke modules get separated and delivered to the shipyard orbital station for further usage or utilization, or both side blocks get delivered to the shipyard for further continuous refuelling and usage.

Spaceplane.

Not a part of the TSTO itself, but main spaceship to deliver humans and particular cargo.
1.5 times smaller that Shuttle.
Total mass 30+ t, crew 4.
Payload compartment can contain 2m wide things.

Lifting body of Spiral/BOR/Dreamchaser shape.

The crew sits in an ejectable cylindroconic capsule 2 m wide, 2 by 2. Like Soyuz RV, but a bit longer.
The capsule is not mounted into the ship like in Shuttle, but is put inside as a part of payload. Though rather than other payloads has front windows.
All 4 seats ejectable ('cuz they can).

The crew capsule is ejectable, too. 
1. Jettison the doors section and engage primary ejection impulse in direction "feet-to-head", throwing the capsule radially for 2 meters,
2. Decouple the lightweight attachment pad and enable main LES engine pushing the capsule forward-away.

To carry more passengers, another same capsule can be put behind the crew capsule. To be ejected one-by-one.

Without capsules the spaceplane is pure cargo with long payload compartment.
So, no cargo/crew modifications, just the same plane with/without a detachable cabin.

The crew cabin is crumped, it's a pure atmospheric cabin, no orbital flight abilities. They just get to/from the orbit inside it.

Behind the cabin - a 2m spherical compartment like Soyuz orbital module or Almaz/OPS native rear EVA module.
Front door - to the cabin, top door - for EVA, bottom door - to the crawl tunnel to the rear cabin, rear door - to a pressurized module in the cargo payload (if any).
Detached in uncrewed flights.

Rear (orbital) cabin. Always present, not detachable. To be used all orbital flight long. All orbital maneuvering is done from here.
3m cylider with rear (in orbit - front) cone and front (in orbit - rear) hemisphere.
2 pilot seats aside the central passage to the docking node on the cone top.
Behind them - toilet and kitchen (1x1 m both, aside the passage).
The hemisphere looks into the payload compartment and has 2 round doors: central - to a pressurized module in the cargo payload (if any), front-down - into a crawl tunnel to the nose part.

Aside the fuselage - two nacelles with tanks and paired engines.
Orbital engines (kerosene+HTP or kerolox or hypergolics) in the nose part of nacelles, aside the front cabin.
Two small turbojets (kerosene) in the rear part of nacelles, aside the rear cabin.
2 retractable air scoops. Blocks of RCS (HTP or kerosene+HTP or hypergolics).

Foldable wings. Folded behind up on launch, expanded in flight or before deorbiting.

Flight duration - 1..2 weeks, just to replace the crew and deliver some goods, not to stay docked.

Edited September 11, 2018 by kerbiloid

[KerikBalm]

On 5/1/2015 at 5:32 PM, Mr Shifty said:

You've just eliminated the Space Shuttle Orbiter.

Generally speaking... good riddance...

That thing as not cost effective. It got 27.5 metric tons to orbit, and had a dry mass of 78 tons. 3/4 of the mass it gets to orbit is simply the vehicle itself and is going to come right back down, that's pretty inefficient. Its even worse if you consider that the external tank makes it nearly to orbit (and could be taken there at the expense of payload: + another 26.5 tons taken to orbit that serves no purpose once in orbit).

Every kg added to the second stage is many more kg added to the first stage. This provides huge incentives for first stage recovery before 2nd stage recovery (not to mention, first stage recovery is much easier). The shuttle was pretty backwards in that respect, focusing on recovery of the orbital stage, discarding a massive tank, and rather crude recovery of the boosters.

I'd like to see a modified concept of the skylon: airbreathing to about mach 5.5, then go closed cycle for another 2km/sec, and then release a 2nd stage to orbit.

Don't bring the airbreathing equipment to orbit. Don't bring empty tanks to orbit, don't bring unnecessary wings to orbit (the shuttle could have used much smaller wings if they weren't committed to being able to return to the launch site right after launching something into a polar orbit).

I'm not saying a reusable 2nd stage is out, but it should be a lower priority than a reusable 1st stage.

Also, that dreamchaser makes more sense than the shuttle... it doesn't really have much wing, its a lifting body (much better for re-entry, lower dry mass), and it doesn't have a heavy payload bay. I suppose its ok as an alternative to something like the soyuz or progress- which aren't even second stages, they are orbital vehicles. Downmas capability is needed for stations as well, and in those circumstances, a lifting body or spaceplane does much better than a capsule.

They have OMS propulsion, but don't really do the work of getting their payload into orbit, they are the payload for the 2nd stage.

[Rakaydos]

Premice: a large advanced-propulsion engine is only useful in space, but needs occasional servicing on earth. (Say, inertial confinement fusion pulse, or similar "it works in the lab right now, not as propulsion" designs.)

Advanced engine section is aerodynamic when 6 spherical fuel tanks are removed and a waterproof fairing applied. there is a 7th fuel tank sufficent to circulrize the engine at an orbital assenbily altitude once out of the atmosphere.

This is lofted by a Seadragon style ocean launch of a methalox booster that returns to launch site after putting the engine section suborbital.

[wumpus]

On 5/1/2015 at 11:32 AM, Mr Shifty said:

You've just eliminated the Space Shuttle Orbiter.

Things that made a Space Shuttle Orbiter that you would never do today:

If you can land (and reuse) a first stage, you will never put "main engines" on a second stage.  That's way too much dead weight going to orbit when you can bring *anything* else with you.  Yes, the shuttle did land and reuse the first stage "engines", but reusing huge steel tubes isn't saving any money.  You want to reuse liquid rockets.

The cargo bay only made sense if you are planning to return a satellite to Earth.  In the unlikely even such might happen, I'd assume that you would make a custom capsule that would fit in the biggest fairing you can find (possibly the "new improved" capsule *is* the fairing to avoid these issues, but that requires complex retro-engineering for stability).

Lose those and you have a dreamchaser.  And it isn't really clear if it has real advantages, just that it is missing most of the disadvantages of the shuttle.

[kerbiloid]

Gemini was true. Others were heresy.

And Almaz, i.e. a post-Gemini counter-Gemini.

 

Say to service a payload after putting into orbit they would just launch a Gemini on top, and no Shuttle would be required.

Edited September 11, 2018 by kerbiloid