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Spacescifi

A Combined Approach Better Than SSTO's?

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Posted (edited)

SpaceX tends to blow away the competition as far as actually building and launching reusable rocketry goes.

Then I noticed what Branson has been up to and I thought... why not combine the two concepts the two billonaires have promoted while adding a bit of my nuclear enthusiam to the mix?

I am beginning to think the whole concept of Earth launched SSTO's wasteful, as I think there is a much better alternative.

 

Here's my idea: Build a flying nuclear airbreathing suborbital vehicle. Note this is NOT an SSTO by any means. What it is is a large cargo aircraft on par with a passenger jet, only designed to fly at suborbital speeds by using whatever mix of turbofans, turbojets, pulsejets, shock cones, and aerospikes that it needs.

Step one: Launch using a nuclear airbreathing propellant mixed powered sled that moves the suborbital cargo plane 500 MPH on the ground, upon which the the suborbital craft detaches and flies away using it's nuclear thermal airbreathing propellant injected turbo linear aerospike engines (like the venture star's).

Step 2: Let the suborbital craft go suborbital then release 50 tons worth of spaceship. So whatever craft that is along for the ride needs to weigh no more than 50 tons, and some of that 50 tons must be propellant tank to reach space.

 

Step 3: What's left of the 50 ton craft (lighter after expelling propellant) reaches orbit.

Step 4: After the mission for reentry the orbiter does reentry and uses engines to rendezvous and dock inside a suborbital aircraft, which ferries it back to the planet spaceport.

My conclusions: I think getting to space is best approached by making craft that are specifically designed to do one thing... help each other out.

Proper heavy cargo SSTO's are dangerous, verified by the most successful version of it if it ever flew (nuclear bomb pusher plate).

 

In other words, I see SSTO's hardly being a thing in the future, but suborbital airbreathing ferries to launch orbiters seems more economical. Build fleets of them if you want to launch enough orbiters to build a station or large orbiting spaceship faster.

As making a true SSTO requires a ship to be a jack of all trades but a master of none, and both air and spaceflight demand optimization which you will never get with a proper SSTO.

 

What are your ideas?

 

Edited by Spacescifi

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Posted (edited)

You're right that SSTO is effectively pointless as it can't carry any meaningful playload, and that two stage to orbit is much better from that perspective of you can make both stages reusable.

But I think nuclear propulsion and wings is overcomplicating. 50t from suborbital is much less playload than a Falcon9. Why not 1200t reusable craft on top of a mammoth reusable booster?

Edited by RCgothic

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2 hours ago, RCgothic said:

You're right that SSTO is effectively pointless as it can't carry any meaningful playload, and that two stage to orbit is much better from that perspective of you can make both stages reusable.

But I think nuclear propulsion and wings is overcomplicating. 50t from suborbital is much less playload than a Falcon9. Why not 1200t reusable craft on top of a mammoth reusable booster?

 

Good point.

So reusuable nuclear airbreathing propellant injection boosters perhaps?

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Posted (edited)

You don't really want a nuclear reactor on anything that has to repeatedly launch or land because sooner or later there'll be an accident. Also nuclear propulsion has poor thrust to weight and the exhaust can be problematic for the launch and landing sites.

Nuclear propulsion is best left to deep-space only. Things don't start getting really radioactive until being turned on for the first time, so the initial launch isn't too much of a risk. But it's not suited to repeated trips through the atmosphere.

We currently don't have any air-breathing engines that work well at high hypersonic speeds. You can get higher, faster, with better payload fraction and use less propellant by using conventional rocket engines.

Edited by RCgothic

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12 hours ago, Spacescifi said:

I am beginning to think the whole concept of Earth launched SSTO's wasteful, as I think there is a much better alternative.

This is true. Anything that would make a great SSTO either has high thrust (making it a great first stage) or high efficiency (making it a great upper stage). Any SSTO concept you can imagine will have better performance if you use it as a first stage booster instead.

The only drawback is that an SSTO gets a "free" RTLS by re-entering after one trip around. With staging you need either reserve propellants for a RTLS boostback or you need downrange recovery assets.

12 hours ago, Spacescifi said:

Step one: Launch using a nuclear airbreathing propellant mixed powered sled that moves the suborbital cargo plane 500 MPH on the ground, upon which the the suborbital craft detaches and flies away using it's nuclear thermal airbreathing propellant injected turbo linear aerospike engines (like the venture star's).

The reason to use a sled is to reduce the mass of the landing gear and the size of the wings, since you no longer need to lift off horizontally at full load and the gear is only used on landing. The problem with this approach is that you lose non-catastrophic abort capability. Conventional rockets are single-use so if you encounter a problem on launch you either limp along to a lower orbit or you simply lose the vehicle, but with a reusable launch vehicle you really need the ability to turn around and fly back if something goes wrong. Can't do that if your gear is too small to land under full load.

12 hours ago, Spacescifi said:

Step 2: Let the suborbital craft go suborbital then release 50 tons worth of spaceship. So whatever craft that is along for the ride needs to weigh no more than 50 tons, and some of that 50 tons must be propellant tank to reach space.

This is essentially the "starter kit" Skylon, using a suborbital version to deliver payloads that then boost into LEO under their own power.

Keep in mind that the fueled Falcon 9 upper stage is 115 tonnes without payload.

12 hours ago, Spacescifi said:

Step 4: After the mission for reentry the orbiter does reentry and uses engines to rendezvous and dock inside a suborbital aircraft, which ferries it back to the planet spaceport.

Frankly this part is a terrible idea, no offense. If the orbiter is capable of re-entry and atmospheric flight it should just glide back on its own.

12 hours ago, Spacescifi said:

In other words, I see SSTO's hardly being a thing in the future, but suborbital airbreathing ferries to launch orbiters seems more economical. Build fleets of them if you want to launch enough orbiters to build a station or large orbiting spaceship faster.

This would become super profitable if there was an independent market for suborbital hypersonic passenger and cargo delivery. Unfortunatelt this does not appear to be a thing.

4 hours ago, Spacescifi said:

So reusuable nuclear airbreathing propellant injection boosters perhaps?

Nukes make a poor first stage, period.

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Posted (edited)
1 hour ago, sevenperforce said:

This is true. Anything that would make a great SSTO either has high thrust (making it a great first stage) or high efficiency (making it a great upper stage). Any SSTO concept you can imagine will have better performance if you use it as a first stage booster instead.

The only drawback is that an SSTO gets a "free" RTLS by re-entering after one trip around. With staging you need either reserve propellants for a RTLS boostback or you need downrange recovery assets.

The reason to use a sled is to reduce the mass of the landing gear and the size of the wings, since you no longer need to lift off horizontally at full load and the gear is only used on landing. The problem with this approach is that you lose non-catastrophic abort capability. Conventional rockets are single-use so if you encounter a problem on launch you either limp along to a lower orbit or you simply lose the vehicle, but with a reusable launch vehicle you really need the ability to turn around and fly back if something goes wrong. Can't do that if your gear is too small to land under full load.

This is essentially the "starter kit" Skylon, using a suborbital version to deliver payloads that then boost into LEO under their own power.

Keep in mind that the fueled Falcon 9 upper stage is 115 tonnes without payload.

Frankly this part is a terrible idea, no offense. If the orbiter is capable of re-entry and atmospheric flight it should just glide back on its own.

This would become super profitable if there was an independent market for suborbital hypersonic passenger and cargo delivery. Unfortunatelt this does not appear to be a thing.

Nukes make a poor first stage, period.

 

No offense taken... I was only trying to save on fuel.

Alright... I am not giving up though.

So nuclear first staging is poor I know. What if we put a nuclear reactor to power an MHD generator for the jet airbreathing rocket booster?

 

Essentially Ayaks powered by nuclear power.

https://en.m.wikipedia.org/wiki/Ayaks

That's the best I can do, is it worth a shot?

And yes... I am deadset on putting a nuclear reactor on a rocket one way or another, even if it is just powering MHD for the airbreathing.

 

Beyond this, I think airbreathing with MHD is the key to better boosters and SSTO's.

Edited by Spacescifi

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10 hours ago, RCgothic said:

You're right that SSTO is effectively pointless as it can't carry any meaningful playload, and that two stage to orbit is much better from that perspective of you can make both stages reusable.

But I think nuclear propulsion and wings is overcomplicating. 50t from suborbital is much less playload than a Falcon9. Why not 1200t reusable craft on top of a mammoth reusable booster?

This, SSTO is nice because you don't have to handle stacking, however the downside is strong penalty on payload. We might get SSTO down the line but they would be for small payloads.
First stage just touch into hypersonic and weight is not as critical because adding one ton to the weight just reduce payload 100-300 kg.
Second stage has to survive reentry from orbit but it don't need much engine power but you want vacuum engines. 

Planes don't have this issue as you can land and refuel. Very long range flights tend to be premium and only work then oil price is low as they also run into the rocket equation, they need more fuel to carry all the extra fuel but they save the stop who also tend to include an plane change at an hub. 
 

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4 hours ago, Spacescifi said:

No offense taken... I was only trying to save on fuel.

Not trying to be a dick, but -- how were you going to 'save on fuel' by launching an entire new first stage to rendezvous with a re-entering orbiter, rather than just letting that orbiter descend all the way to the runway without using any fuel at all?

4 hours ago, Spacescifi said:

So nuclear first staging is poor I know. What if we put a nuclear reactor to power an MHD generator for the jet airbreathing rocket booster?

Essentially Ayaks powered by nuclear power.

https://en.m.wikipedia.org/wiki/Ayaks

That's the best I can do, is it worth a shot?

And yes... I am deadset on putting a nuclear reactor on a rocket one way or another, even if it is just powering MHD for the airbreathing.

Beyond this, I think airbreathing with MHD is the key to better boosters and SSTO's.

MHD only works in the ionosphere where the atmosphere is already ionized. It will not work in the mesosphere or below.

You should read about The Air-Breather's Burden.

Also this old thread.

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Posted (edited)

Wardenclyffe towers. Beaming the energy from the on-gorund and/or orbital nuclear powerplants.

The true Tesla instead of using Tesla's name for PR of non-Tesla cars.

Edited by kerbiloid

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17 hours ago, RCgothic said:

You don't really want a nuclear reactor on anything that has to repeatedly launch or land because sooner or later there'll be an accident. Also nuclear propulsion has poor thrust to weight and the exhaust can be problematic for the launch and landing sites.

Not true. In fact, you want to make your nuclear reactor reusable. TWR issues are not common to all NTRs, NERVA (which is what most people think about when they hear about it) was an orbital engine. It's like judging chemical propulsion by what the RL-10 can do. It's relatively straightforward to make a reactor which can survive most possible accidents without a radiation release, but the real problem is that a reactor is friggin' expensive. A disposable nuclear reactor of any kind is wasteful, because these things can run for years.

A simpler way would be to have a nuclear near-SSTO (can be something like Ajax), and attach a small kick/maneuvering stage to the payload. We already have rockets that are nearly single-stage, but use a small, solid or hypergolic upper stage to complete orbital insertion. It's efficient, doesn't leave too much junk in orbit, and it's easier from the mission planning perspective, especially if it's a high precision hypergolic stage.

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29 minutes ago, Dragon01 said:

Not true. In fact, you want to make your nuclear reactor reusable. TWR issues are not common to all NTRs, NERVA (which is what most people think about when they hear about it) was an orbital engine. It's like judging chemical propulsion by what the RL-10 can do. It's relatively straightforward to make a reactor which can survive most possible accidents without a radiation release, but the real problem is that a reactor is friggin' expensive. A disposable nuclear reactor of any kind is wasteful, because these things can run for years.

A simpler way would be to have a nuclear near-SSTO (can be something like Ajax), and attach a small kick/maneuvering stage to the payload. We already have rockets that are nearly single-stage, but use a small, solid or hypergolic upper stage to complete orbital insertion. It's efficient, doesn't leave too much junk in orbit, and it's easier from the mission planning perspective, especially if it's a high precision hypergolic stage.

I didn't say not reusable. I said "not repeatedly flying through the atmosphere and repeatedly intersecting the ground." Reuse nuclear propulsion stages as much as you like. Just keep them away from Earth.

I am very much in favour of doing useful things with nuclear propulsion and building a bajillion reactors for clean energy. I am very much not in favour of doing risky things with nuclear propulsion.

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It's not risky. NERVA survived being blown up without contaminating everything. A space-only tug is a pretty great use for an NTR, too (you can really make the Isp work in this application), but not the only one. A nuclear reactor is a fairly robust thing, and it's quite possible to design it so that it's reasonably crash-proof, even up to terminal velocity. 

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3 hours ago, Dragon01 said:

it's quite possible to design it so that it's reasonably crash-proof, even up to terminal velocity. 

i?id=4bdd0dd1734aae66ebac13fa1beebe3f-l&:sticktongue:

Recovering a sunken nuclear turbojet might be problematic, though.

571c498103.jpg

 

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As demonstrated, it's better to leave it there instead of trying to dredge it out.  :) In that particular case, if they didn't do it, the US probably would at some point (or at least send a sub with underwater drone to check it out), and they obviously wouldn't want that. For a commercial LV, it wouldn't be economical to attempt recovery, especially from the ocean.

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On 4/4/2020 at 5:18 AM, RCgothic said:

You're right that SSTO is effectively pointless as it can't carry any meaningful playload, and that two stage to orbit is much better from that perspective of you can make both stages reusable.

But I think nuclear propulsion and wings is overcomplicating. 50t from suborbital is much less playload than a Falcon9. Why not 1200t reusable craft on top of a mammoth reusable booster?

The 650 ton Airbus A380 is going out of production, while the 50-80 ton non-max 737 has been extremely successful.  Of course if you have a single destination of "Low Earth Orbit" (or possibly "just beyond the Van Allen belts"), perhaps you will do better with a much larger craft.  Although I suspect that a Falcon 9 might match a Ford Trimotor as a better historical analog.

- note the numbers are for the total weight of the aircraft: assume roughly half of that as payload (unless going London-Sydney, where you need almost half the weight as fuel).

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Posted (edited)

You can't just compare masses of airliners and rockets. (By the way 737max is roughly 1/4 payload at max takeoff mass).

Falcon 9 is the single most popular launch platform worldwide bar none. The F9 upper stage masses approx 112t wet including 16t heaviest payload actually flown. It stages high (80km) and fast (Mach 6) so that in likelihood an aircraft-launched upper stage is going to have to work much harder

So a reusable upper stage less than half the mass of F9 upper stage is going to have less than half the payload and tighter margins, even before you include the effort of making it reusable (F9US is not reusable). Tighter margins means the vehicle has to work harder, which makes it less reusable.

It's no coincidence that the two new reusable craft on the drawing board - starship/superheavy and New Glenn are both going larger than Falcon9.

Edited by RCgothic

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Posted (edited)

There are a lot of different ways of measuring how good a launch vehicle is. You can do it financially (unit cost, development cost, operational cost); by rocket performance (payload fraction, fuel usage, specific impulse, specific engine power, energy efficiency); or by time (time from contract to orbit, integration time, vehicle production time, facility production time, vehicle turnaround time, facility turnaround time, throughput)

How good a vehicle is also highly depends on what you are trying to accomplish (LEO, GTO, Moon, Mars) and how developed your technologies and infrastructures are.

Currently, there are no fully reusable launch vehicles, SSTOs, air-breathing spaceplanes, nuclear thermal rockets, or high powered ion thrusters. Thus today, partially reusable rockets seem to have the best cost per kg. But expendable rockets have superior throughput and payload fractions, owing to simpler vehicles and only needing ideal weather at the launch location.

If all feasible future technologies are allowed, then a dynamically supported orbital ring is the best surface to orbit transport, as they can take thousands of kilotons up per day at a few cents per kilogram.

For anything in between, it really depends on what we develop first.

In the near term, full reusability will join the competition with partial reusable and expendable rockets. As refurb costs go down and numbers of flights increase, reusable vehicles will out compete expendables. Precooled jet engines, such as those on Skylon, will start competition between reusable rockets and space plane TSTOs. Technologies like air-augmented rockets, pulse detonation engines, and dual ramjet-scramjets would continue to fuel competition. While SSTOs would be possible at this point, they wouldn't be practical until the development of laser thermal launch vehicles. These would take over the small sat market, but rockets and spaceplanes would continue to dominate for larger launches. This would continue until the skyhooks capable of lifting several dozen tons are put in orbit, at which point chemical rockets will be put out of the running, and only spaceplanes and LTLVs remain. Air breathing laser craft, if developed, would quickly rise over the other two, as it wouldn't require an onboard propellant.

An airbreathing nuclear TSTO spaceplane is certainly better than existing technologies, but will probably be made obsolete before they are ever developed.

 

Edited by wafflemoder
posted by mistake before finished

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10 hours ago, wafflemoder said:

There are a lot of different ways of measuring how good a launch vehicle is. You can do it financially (unit cost, development cost, operational cost); by rocket performance (payload fraction, fuel usage, specific impulse, specific engine power, energy efficiency); or by time (time from contract to orbit, integration time, vehicle production time, facility production time, vehicle turnaround time, facility turnaround time, throughput)

How good a vehicle is also highly depends on what you are trying to accomplish (LEO, GTO, Moon, Mars) and how developed your technologies and infrastructures are.

Currently, there are no fully reusable launch vehicles, SSTOs, air-breathing spaceplanes, nuclear thermal rockets, or high powered ion thrusters. Thus today, partially reusable rockets seem to have the best cost per kg. But expendable rockets have superior throughput and payload fractions, owing to simpler vehicles and only needing ideal weather at the launch location.

If all feasible future technologies are allowed, then a dynamically supported orbital ring is the best surface to orbit transport, as they can take thousands of kilotons up per day at a few cents per kilogram.

For anything in between, it really depends on what we develop first.

In the near term, full reusability will join the competition with partial reusable and expendable rockets. As refurb costs go down and numbers of flights increase, reusable vehicles will out compete expendables. Precooled jet engines, such as those on Skylon, will start competition between reusable rockets and space plane TSTOs. Technologies like air-augmented rockets, pulse detonation engines, and dual ramjet-scramjets would continue to fuel competition. While SSTOs would be possible at this point, they wouldn't be practical until the development of laser thermal launch vehicles. These would take over the small sat market, but rockets and spaceplanes would continue to dominate for larger launches. This would continue until the skyhooks capable of lifting several dozen tons are put in orbit, at which point chemical rockets will be put out of the running, and only spaceplanes and LTLVs remain. Air breathing laser craft, if developed, would quickly rise over the other two, as it wouldn't require an onboard propellant.

An airbreathing nuclear TSTO spaceplane is certainly better than existing technologies, but will probably be made obsolete before they are ever developed.

 

 

Fascinating.

I am not sure what an orbital ring is, but I suspect it is like a space elevator that is built in geostationary orbit. Only a ring right?

For anyone who does not know, all geostationary orbit means is that an object is just far away enough from Earth and is at a sufficient speed that it circles (orbits) the Earth within a 24 hour period. Which is a big differencs compared to circling every 90 min as stuff does in Low Earth Orbit (LEO).

That means for space elevator applications, all you need is a mass heavy enough in geostationary orbit and bunch of cables connected to Earth and bam!

We just made Jack and the beanstalk for reals! Or at least as real as possible.

 

Assuming an orbital ring is what I think it is, it would cost likely decades of resources to construct, maybe a century or more to finish it.

Only a super dedicated space programcl could do that.

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Comparing space elevator to an orbital ring is like comparing this:

s-l640.jpg

to this:

world-s-largest-container-ship-msc-gulsu

They both are used for transporting goods, but one is slightly bigger.

Orbital ring is placed in low earth orbit, not geostationary.

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Posted (edited)

I may be late to a party, but a while ago, I had read a NASA study on a SSTO booster named 'Antares' which used chemical propulsion. The engine used was a dual thrust mode engine, in which by changing the fuel-ox ratio and nozzle diameter, the thrust and ISP could be changed. Initially the rocket will operate on a high thrust mode, and then once the acceleration has reached a specified value, it will switch to high ISP mode.

http://hdl.handle.net/2060/19920011425

EDIT: It burns the tankage while returning and only lands the engines in one piece. So it may not be a SSTO. It could transfer 10 tons to LKO in this mode.

Another SSTO concept, using chemical propulsion would be the StarRaker, which used Jet engines and SSMEs in tandem to transfer 100 tons to orbit each flight.

Edited by Selective Genius

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