Author Topic: Which is ultimately better, reusable rockets vs. spaceplanes?  (Read 6984 times)

Offline Clueless Idiot

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Which one in the end will allow us to get more tonnage into LEO for the lowest cost? Which one can scale bigger than the other? I'm assuming rockets can scale bigger than a spaceplanes can (since Elon stated that eventually they'll have a rocket that'll dwarf even the ITS).

Offline hkultala

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Depends too much the actual technology involved, so that there cannot be a good general answer for most parts.

Spaceplane practically requires SABRE-style engine to be reasonable.

And it's easier to scale rockets into big size.

Also going to higher than LEO is very hard and inefficient for spaceplanes, but a separate space tug can be used to get payload to higher orbit more effectively.
« Last Edit: 06/02/2017 11:21 AM by hkultala »

Offline Hankelow8

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Spaceplane technology only really works when you are launching a 100 or more satellites a month, not a year.

It will take many years to reach this level, that's when the business plan for spaceplanes works.

Regards reaching higher orbits, that's when space tugs refuelled in orbit by spaceplanes do the job very nicely.

Regretfully Skylon was ahead of its time, this does not mean air-breathing rockets engines are not relevant for today, for the moment more like high-speed cruise in the upper atmosphere, which the Reaction engine is due to start testing an engine in 2019.

 

Offline Clueless Idiot

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Well what about what Virgin Galactic's approach but scaled to way bigger, I mean huge, I mean a much bigger carrier plane and spaceplane, could this ever beat rockets?

Offline john smith 19

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Which one in the end will allow us to get more tonnage into LEO for the lowest cost?
Excellent choice of question. It is indeed all about the money.

One thing your question does leave out is at what size of package does that price apply?

Musk talks of < $1000/lb but that's for a fully used FH to LEO at a flight rate of 4 a year.

Note a rocket needs a lot of infrastructure and a lot of mfg facilities. The difference between a rocket and a spaceplane concept is that a properly designed spaceplane can be launched by multiple countries by multiple owners.   It will probably be capable of self ferry and deliver those prices at much below the fully loaded vehicle a rocket operator needs to give you that price per lb. It's the owners who decide how often any given plane flies but with a rocket the mfg is the owner.  Something that does not happen in any other industry.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline john smith 19

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Well what about what Virgin Galactic's approach but scaled to way bigger, I mean huge, I mean a much bigger carrier plane and spaceplane, could this ever beat rockets?
Paul Allen has unveiled Stratolaunch, which is designed to carry a 550 000lb (250tonne) rocket. However AFAIK it's not had its maiden flight yet.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Jarnis

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Wings are silly in space. Rockets provably can land like they always were meant to - on a pillar of flame, tail first. Hence, spaceplanes are pretty silly.

Offline IRobot

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The only advantages of spaceplanes are during take off and landing.
In takeoff because they could potentially land back in case of non catastrophic failure, avoiding loss of payload.
In landing, because it is easier to handle and less stress on structure.

There is also the advantage of flying to a different latitude to match orbital plane.

But... those advantages could be soon gone. Landing seems to be mastered by SpaceX.
And a large ITS-scale vessel could probably still be able to recover from a launch issue.
Orbital plane match can be compensated on rockets by just burning more fuel or handling less weight.

Besides that, spaceplanes are just a mess. Weight distribution throughout the flight is hard to manage. Payload will always be much smaller compared to rockets. Skylon is already 80 meters long for less than 20t of payload. Development is probably much more costly and takes more time.


Online dror

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My defenition for a spaceplane (what is yours?) is jet engine and wings.
Assuming reusability can reduce the cost of luanch to ~the price of fuel+refurbishment, spaceplanes may set a lower price due to:
less fuel needed with the much higher ISP of jet engines and
less refurbishment needed due to more lofted entry.
« Last Edit: 06/02/2017 01:14 PM by dror »
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Offline Hankelow8

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Wings are silly in space. Rockets provably can land like they always were meant to - on a pillar of flame, tail first. Hence, spaceplanes are pretty silly.

If wings help a spaceplane take off Horizontally and allow a return to base if a problem develops they are not silly.

 If wings help a spaceplane land anywhere it wants on more or less a normal runway it's not silly.

Offline Rocket Science

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Insufficient data at this point...
"The laws of physics are unforgiving"
~Rob, Physics instructor, aviator, vintage auto racer

Online JasonAW3

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Sadly, as I am a fan of spaceplanes, I have come to some unfortunate conclusions;

Unless designed as a lifting body, filling every cubic centimeter of volume and making every gram of mass with usable equipment, consumables and fuel, rockets win. 

Even if every bit of a space plane has an alternative use, such as heat sinks for the wings, or extra storage for the landing gear wheel wells, rockets, being purpose built for ONLY one real purpose, still have the advantage.
My God!  It's full of universes!

Offline Rocket Science

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At this point I don't recall any rocket that has been recovered and re-used returning from an orbital velocity...
"The laws of physics are unforgiving"
~Rob, Physics instructor, aviator, vintage auto racer

Online edkyle99

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Which one in the end will allow us to get more tonnage into LEO for the lowest cost? Which one can scale bigger than the other? I'm assuming rockets can scale bigger than a spaceplanes can (since Elon stated that eventually they'll have a rocket that'll dwarf even the ITS).
SpaceX has shown how first stage VTVL might be done (they're still perfecting the idea).  Others are planning to try their hand at the concept.  NASA wanted to do a spaceplane-like flyback first stage for Shuttle, but it cost too much to develop.  It seems that VTVL has won the argument for Stage 1 flight (but don't tell the DARPA XS-1 contractors).

That leaves Stage 2.  TBD!

 - Ed Kyle
« Last Edit: 06/02/2017 02:30 PM by edkyle99 »

Offline IRobot

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My defenition for a spaceplane (what is yours?) is jet engine and wings.
Topic is spaceplane, not airlaunch, so jet engine is not enough.

Assuming reusability can reduce the cost of luanch to ~the price of fuel+refurbishment, spaceplanes may set a lower price due to:
less fuel needed with the much higher ISP of jet engines and
less refurbishment needed due to more lofted entry.
Fuel price is insignificant.
Regarding refurbishment, a spaceplane is always more complex than a rocket, so I don't you can just claim that refurbishment is cheaper.

Online dror

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My defenition for a spaceplane (what is yours?) is jet engine and wings.
Topic is spaceplane, not airlaunch, so jet engine is not enough.

Assuming reusability can reduce the cost of luanch to ~the price of fuel+refurbishment, spaceplanes may set a lower price due to:
less fuel needed with the much higher ISP of jet engines and
less refurbishment needed due to more lofted entry.
Fuel price is insignificant.
Regarding refurbishment, a spaceplane is always more complex than a rocket, so I don't you can just claim that refurbishment is cheaper.
-Jet - Skylon is a planed spaceplane which uses jet engin for the first part of it's flight. Obviously not enogh but otherwise it's just a rocket.
-Fuel prices - Elon Musks stated the goal of making spaceflight prices to the order of magnitude of fuel prices. He repeats that over and over. Saying that that is insignificant is shortsighted.
-refurb- Jet engines now operate for thousands of hours and rockets dont.
Wings will allow lower G forces on launch and reentry
Being more complex doesn't reflect on refurbishment.
.
« Last Edit: 06/02/2017 07:29 PM by dror »
"If we crave some cosmic purpose, then let us find ourselves a worthy goal. "
Carl Sagan, Pale Blue Dot

Offline rayleighscatter

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Regarding refurbishment, a spaceplane is always more complex than a rocket, so I don't you can just claim that refurbishment is cheaper.
Not necessarily true. If space travel were to become as common as everyone would like, then refurbishing a spaceplane with 1 or 2 larger engines could easily be cheaper than refurbishing a reusable rocket with 9 (or more engines).

Offline KelvinZero

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Just want to say I think the "almost mundane" F9R/ITS/Blue Origin approach has a lot of potential for growth.

Space planes could suddenly find an investor tomorrow, or people could shy away for another half century because the two stage approach just keeps being the place to invest for reliable return and improvement.

I think there is a good chance that by the time someone can prove spaceplanes are ultimately better, it is no longer a race between rockets and spaceplanes anyway. There are lots of other ideas floating around. (Eg ITS upper stage with some sort of rail launcher to put it comfortably into the SSTO range? Not pushing that, just saying it will probably be a different situation that invalidates the comparison)

Offline Gliderflyer

At this point in time I don't think there is enough data on operational RLVs to determine which is better in terms of cost (safety is another story). Both VTVL and HTOL rocket vehicles of (relatively) comparable performance have demonstrated low cost operations with turnaround times less than an hour (although at a small, subsonic scale), and on paper it is easy to scale up either architecture. The issue is that the large amount of unknown variables make it easy to massage the numbers and make a paper rocket in either architecture that is better. Personally I think there are markets for both types of systems, but until we have more data on operational vehicles it is hard to say which is better from a cost perspective.
I tried it at home

Offline john smith 19

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Both VTVL and HTOL rocket vehicles of (relatively) comparable performance have demonstrated low cost operations with turnaround times less than an hour
I'm scratching my head to think what you're talking about?
 The only thing that comes to mind is the Rocket Relay League work that XCOR did but then I'm wondering what the VTOL you would be using for comparison is.

"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

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