Author Topic: Feasibility of a Raptor SSTO and Comparisons to A Fully Reusable Launch System  (Read 20961 times)

Offline dante2308

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I suppose this topic deserved its own thread in the sense that it was a bit more than a conversation about 'possible configurations for Raptor-based rockets.'

Again, I'd like to do the math when I have time, but I am aware that SpaceX has already met the dry mass fractions required to put a non-zero payload in orbit with an SSTO with the intended specs of the Falcon Heavy boosters.

The reason one stages a rocket is to increase (or make non-negative) the payload fraction. However, when we add reusability to the equation, the first stage RTLS actual invites a disadvantage in delta-v which may or may not exceed the disadvantage of SSTO. Even if the two are not on the same order, the feasibility for rapid reusability and manufacturability of an SSTO may exceed the TSTO model and thus generate a potential cost savings.

Does anyone have any thoughts on the matter? Some numbers might greatly aid the discussion as well.
« Last Edit: 11/16/2013 07:46 PM by dante2308 »

Online Elmar Moelzer

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I hope that Gary will find the time to chime in on this. He is my "hero" when it comes to SSTO RLVs. I think it is very doable with a non zero payload on a reasonably sized LV. You are right that the return to launch site cuts significantly into the payload. I am not sure that it is more than a TSTO with first stage RTLS, but the difference might be small enough that the improved handling of an SSTO outweights the payload penalty.
If you do something like the Phoenix, you can save on a lot of aspects of LV operations compared to a TSTO.

Offline simonbp

It's not that hard to make an SSTO, but it is very hard to make an SSTO that will reenter and land in one piece. A Delta IV first stage launched alone could make it to orbit, but that would no longer be the case if you added enough recovery gear to it that it would make it down to the ground intact.

The two-stage approach that SpaceX have taken is attractive because most of the vehicle can be recovered without having to worry about covering the first stage in heavy reentry-grade TPS. It may take a significant advance in TPS to really make an SSTO worth it.

Offline Rabidpanda

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A vehicle that is mostly empty tanks won't need as much TPS as a capsule like Dragon.

One challenge would be using the engines at multiple altitudes. I see several options:
1. Use engines that are optimized for somewhere between sea level and vaccuum and take the performance hit.
2. Use two different types of engines on one vehicle, i.e. 8 Raptors with 1 Raptor Vacuum.
3. Use a design that compensates for the altitude, such as an expansion deflection nozzle.

Offline PlanetStorm

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It's not that hard to make an SSTO, but it is very hard to make an SSTO that will reenter and land in one piece. A Delta IV first stage launched alone could make it to orbit, but that would no longer be the case if you added enough recovery gear to it that it would make it down to the ground intact.

The two-stage approach that SpaceX have taken is attractive because most of the vehicle can be recovered without having to worry about covering the first stage in heavy reentry-grade TPS. It may take a significant advance in TPS to really make an SSTO worth it.

I wonder if you are missing the point of the OP.  My reading of it is that the OP is weighing a TSTO with reusable first stage against a non-reusable SSTO. Both approaches have the disadvantage of cutting deeply into payload compared to a non-reusable TSTO, but both have advantages too. The non-reusable SSTO has the advantage of simplicity, whereas the two stage has the advantage of reusability of (at least) the first stage. So the question of the OP is, which approach wins in the economic stakes?

Of course, I might have misunderstood the OP too ;)

 

Offline TaylorR137

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Boosted SSTO makes the most sense. The boosters are reusable and flyback, the core refuel-able in LEO.

Offline Rabidpanda

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Boosted SSTO makes the most sense. The boosters are reusable and flyback, the core refuel-able in LEO.

This may be just semantic, but if you have boosters then it's not an SSTO. Otherwise the shuttle would have been considered an SSTO.

Offline guckyfan

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Boosted SSTO makes the most sense. The boosters are reusable and flyback, the core refuel-able in LEO.

This may be just semantic, but if you have boosters then it's not an SSTO. Otherwise the shuttle would have been considered an SSTO.

It's more than semantics. If you have boosters you have staging events. You have to integrate components on the ground. So you lose every advantage a SSTO might have operationally.

Offline ChrisWilson68

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Boosted SSTO makes the most sense. The boosters are reusable and flyback, the core refuel-able in LEO.

Boosted Single-Stage-To-Orbit is the definition of Two-Stage-To-Orbit.

Offline ChrisWilson68

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I suppose this topic deserved its own thread in the sense that it was a bit more than a conversation about 'possible configurations for Raptor-based rockets.'

Again, I'd like to do the math when I have time, but I am aware that SpaceX has already met the dry mass fractions required to put a non-zero payload in orbit with an SSTO with the intended specs of the Falcon Heavy boosters.

The reason one stages a rocket is to increase (or make non-negative) the payload fraction. However, when we add reusability to the equation, the first stage RTLS actual invites a disadvantage in delta-v which may or may not exceed the disadvantage of SSTO. Even if the two are not on the same order, the feasibility for rapid reusability and manufacturability of an SSTO may exceed the TSTO model and thus generate a potential cost savings.

Does anyone have any thoughts on the matter? Some numbers might greatly aid the discussion as well.

I believe SpaceX has said the first stage is 70%-80% of the cost of a Falcon 9.  It's hard to see how a SSTO could be much simpler and cheaper than a F9 first stage.  So SSTO reduces costs by (at best) 20%-30% versus TSTO while first-stage-reuse reduces them by 70%-80%.  And the payload cut for F9 first stage reuse is reported 15%-30%.  So, even if the SSTO F9 first stage lofted the full F9 payload, it would still be more expensive as an expendable than the two-stage F9 with first stage re-use.  And, of course, it would be wildly optimistic to say the F9 first stage could be made SSTO with full F9 payload.

My point is that it's easy to get an upper bound that suggests that with anything like today's chemical rocket technology, first-stage reuse in a two-stage system is far cheaper than an expendable SSTO.

Offline 93143

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first-stage-reuse reduces them by 70%-80%.

That only works if the cost to manufacture the stages is the only cost associated with the launch.  Using your model, a Falcon 9 launch with both stages reused would be completely free of charge.

Offline mlindner

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I'm not sure on the argument of a SSTO with reuse versus a TSTO with full reuse. You save greatly on TPS mass by only putting it on sections that actually have to deal with hypersonic re-entry. Also, the complication of a single staging mechanism isn't that bad, especially if it doesn't use any explosives to do so.

Granted you save some tank-end mass (four tank-ends removed) and engine mass, but you lose a lot in extra TPS and strengthening, not to mention tank dead weight being brought to orbit. TSTO also allows incremental re-use rather than either full re-use or complete non-re-use.
« Last Edit: 11/17/2013 10:31 AM by mlindner »
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Offline dante2308

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I was comparing a reusable SSTO to a fully reusable (first and second stage) TSTO. You can't avoid a TPS with either configuration. Any other combination is still on topic. SSTO needs some attention and exploration anyway.

Offline dante2308

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I'm not sure on the argument of a SSTO with reuse versus a TSTO with full reuse. You save greatly on TPS mass by only putting it on sections that actually have to deal with hypersonic re-entry. Also, the complication of a single staging mechanism isn't that bad, especially if it doesn't use any explosives to do so.

Granted you save some tank-end mass (four tank-ends removed) and engine mass, but you lose a lot in extra TPS and strengthening, not to mention tank dead weight being brought to orbit. TSTO also allows incremental re-use rather than either full re-use or complete non-re-use.

You also have to carry extra fuel and oxidizer for the first stage to return to the launch site plus the second stage engine and interstage. You can get pretty tricky with the heat shield diameter but PICA-X doesn't weigh that much. By not weigh much, I mean you can cover a meter square with about 5 kg. In fact it's so light, it's almost not even worth debating. It is less than the mass of the RTLS fuel in any case.

My calculations are progressing. Adding drag now....
« Last Edit: 11/17/2013 01:59 PM by dante2308 »

Offline neviden

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Elon has talked in one of his interviews about reusability and has pointed out that it has everything to do with how big of a fraction of your rocket can you deliver to orbit. Reusabiliy part will take about 2%. If you can make your rocket deliver 4%, then you can deliver 2% and still get your rocket back. It's much easier to get robust and reliable 4% TSTO than SSTO.
`
So, if can we make a robust SSTO that goes well over 2%, then it can work. Can we and at what price?

Offline cleonard

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Elon has talked in one of his interviews about reusability and has pointed out that it has everything to do with how big of a fraction of your rocket can you deliver to orbit. Reusabiliy part will take about 2%. If you can make your rocket deliver 4%, then you can deliver 2% and still get your rocket back. It's much easier to get robust and reliable 4% TSTO than SSTO.
`
So, if can we make a robust SSTO that goes well over 2%, then it can work. Can we and at what price?

I have a feeling that once you total up all needed extra's for reusability the delivered mass fraction will be quite small or even negative.   
 

Offline Jcc

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The only SSTO design that has a decent chance of working is as far as I can see is Skylon, but that is still several years before it can be tested. They still need to prove the engines can work. The idea that a big low density airframe can reenter at hypersonic speeds, be strong enough to withstand dynamic pressure and heat without the need for an ablative TPS needs to be proven.

Elon is skeptical about air breathing launch vehicles in general, but I think he wouldn't consider the technology too closely since it can't scale up to MCT class or go BEO, so why bother?

Offline dante2308

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To service the 100% of the launch market that isn't colonizing Mars?

Offline beancounter

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The only SSTO design that has a decent chance of working is as far as I can see is Skylon, but that is still several years before it can be tested. They still need to prove the engines can work. The idea that a big low density airframe can reenter at hypersonic speeds, be strong enough to withstand dynamic pressure and heat without the need for an ablative TPS needs to be proven.

Elon is skeptical about air breathing launch vehicles in general, but I think he wouldn't consider the technology too closely since it can't scale up to MCT class or go BEO, so why bother?

Several years?  That's a bit of an understatement if ever there was one.  They're still developing a test version of the engine let alone the vehicle to go with it.  I'd reckon they'll be lucky to get there under 10 years.  How long have they been going so far?  In fact, I'll go so far as to predict that Elon'll be on Mars before Skylon takes to the sky with an operational vehicle  ;)
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Offline IRobot

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Given Skylon's projected cost, IMO it will never be built, even if the engine works.

Offline dante2308

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Calculated the Isp for Raptor engine at 320s SL, 356s vac. Any objections?

Offline deltaV

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Calculated the Isp for Raptor engine at 320s SL, 356s vac. Any objections?
What sort of nozzle, first stage or vacuum?

Offline dante2308

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Calculated the Isp for Raptor engine at 320s SL, 356s vac. Any objections?
What sort of nozzle, first stage or vacuum?

First stage. 1m radius. It kind of depends on the camber pressure they achieve with staged combustion.
« Last Edit: 11/18/2013 06:45 PM by dante2308 »

Offline baldusi

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Reusable SSTO could be also tried with a full stage CH4/LOX rocket with composite tanks. Common bulkhead is trivial for this combo, the LNG part is already developed, you'd only need the LOX composites. A FS LNG/LOX with a chamber pressure of 60MPa would do something like 360s/385s SL/Vac! And have an amazing T/W for that technology, probably at 130 or even higher. Of course it would be an expensive rocket, but the mix of very high pmf and high isp should enable a reusable SSTO. BTW, it could well evolve from the Raptor family.

Offline Rabidpanda

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How would you get sea level Isp that high?

Offline dante2308

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Edit: Superseded by next post.
« Last Edit: 11/19/2013 06:45 AM by dante2308 »

Offline dante2308

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Superseded by more accurate calculations.
« Last Edit: 12/15/2013 03:45 PM by dante2308 »

Offline hkultala

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Sorry about the roughness. Here is my first calculated orbit:

Launch from Florida:
The initial acceleration is 2.65101426361 m/s^2
The initial thrust percent is 100
The initial number of engines cut off are 0 out of 5
Main Engine Cut OFF
The time is 348.21 seconds
Velocity is 7.87330442438 km/s
Altitude is 134.127262879 km
The final acceleration is 9.44607675087 m/s^2
The final thrust percent is 99
The final number of engines cut off are 0 out of 5
Orbit Achieved!! Circular orbit velocity was 7.83321791163 km/s
Current mass is 18.2961705186 tons
The apogee (max Earth radius) is 524.819854367 km
The perigee (max Earth radius) is 117.608332424 km
The inclination is 27.8052772316 degrees

Obviously this isn't optimal yet and I can get a little more mass to an even higher orbit if i play with it a bit. What do you think about the numbers?

117 km perigee sound like it's going to drop after couple of orbits due atmospheric drag, not very good orbit.


Offline dante2308

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Sorry about the roughness. Here is my first calculated orbit:

Launch from Florida:
The initial acceleration is 2.65101426361 m/s^2
The initial thrust percent is 100
The initial number of engines cut off are 0 out of 5
Main Engine Cut OFF
The time is 348.21 seconds
Velocity is 7.87330442438 km/s
Altitude is 134.127262879 km
The final acceleration is 9.44607675087 m/s^2
The final thrust percent is 99
The final number of engines cut off are 0 out of 5
Orbit Achieved!! Circular orbit velocity was 7.83321791163 km/s
Current mass is 18.2961705186 tons
The apogee (max Earth radius) is 524.819854367 km
The perigee (max Earth radius) is 117.608332424 km
The inclination is 27.8052772316 degrees

Obviously this isn't optimal yet and I can get a little more mass to an even higher orbit if i play with it a bit. What do you think about the numbers?

117 km perigee sound like it's going to drop after couple of orbits due atmospheric drag, not very good orbit.
The slightest burn at apogee will fix that. This is about mass. The only variable I used was the number of Raptors. Everything else was optimized for that. The orbit has quite enough energy for LEO. I didn't have the time to go in and make the very fine corrections needed to put it in a higher perigee. Also note that the actual perigee is closer to 134 km about the time of maximum inclination.

I want to emphasize the lack of assumptions again. I optimized Isp straight from thermodynamics and chemistry. That drag you speak of is built into the code, the earth is oblate, initial conditions change with latitude and longitude, the Isp depends on the local density and pressure, and the drag force depends on relative velocity, Mach number, shock temperature, and altitude.
« Last Edit: 11/19/2013 12:47 PM by dante2308 »

Offline e of pi

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So the final mass placed into orbit is 18.3 tons, out of...how many? Back calculating from your earlier-stated ISp of 320 SL and 356 vac (which I assume you used here) and the initial 5 engines at (300,000 kgf) * (320/356),  I got that to have the initial acceleration of (9.81+2.65) m/s^2 you note, the vehicle would be about 400,000 kg on the pad. That means about 4.6% of the gross mass is tanks, engines, structure, TPS, and payload. That seems, in my opinion, to be more aggressive a target than is reasonable.

Offline baldusi

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How would you get sea level Isp that high?
Full staged combustion to enable a 60MPa chamber pressure. RD-191 is about 25, NK-33 and RD-0162 are about 17. So even for sea level you'd have enormous expansion ratio. Say, like 100:1 or even more. And yes, that would be for Sea Level.

Offline dante2308

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So the final mass placed into orbit is 18.3 tons, out of...how many? Back calculating from your earlier-stated ISp of 320 SL and 356 vac (which I assume you used here) and the initial 5 engines at (300,000 kgf) * (320/356),  I got that to have the initial acceleration of (9.81+2.65) m/s^2 you note, the vehicle would be about 400,000 kg on the pad. That means about 4.6% of the gross mass is tanks, engines, structure, TPS, and payload. That seems, in my opinion, to be more aggressive a target than is reasonable.

It's too aggressive. It's within Spacex's current architecture, but no, I don't support SSTO now. We need greater Isp engines with high thrust.
« Last Edit: 11/19/2013 10:11 PM by dante2308 »

Offline QuantumG

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It's too aggressive. It's within Spacex's current architecture, but no, I don't support SSTO. F = Isp*Veff*mdot so keeping mdot the same, you get a non-linear relationship between force and Isp.

.. but your turnaround time for the entire vehicle is vastly faster, possibly even just gas-and-go, and your ground infrastructure requirements are vastly less, possibly even just a refueling truck.

The question of fully reusable SSTO is one of plausibility, not utility. If you could get a reusable SSTO to work, with even a marginal payload, someone would find a use for it.

If you could build a first stage of a reusable TSTO that could also operate in reusable SSTO mode, you'd have the best of both worlds.
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline go4mars

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It's too aggressive. It's within Spacex's current architecture, but no, I don't support SSTO. F = Isp*Veff*mdot so keeping mdot the same, you get a non-linear relationship between force and Isp.

.. but your turnaround time for the entire vehicle is vastly faster, possibly even just gas-and-go, and your ground infrastructure requirements are vastly less, possibly even just a refueling truck.

The question of fully reusable SSTO is one of plausibility, not utility. If you could get a reusable SSTO to work, with even a marginal payload, someone would find a use for it.

If you could build a first stage of a reusable TSTO that could also operate in reusable SSTO mode, you'd have the best of both worlds.
Or first stage lands, someone throws an ablative tarp on top, second stage lands on the first.  Or something else efficient (and more plausible like a crane and click-in connections).
« Last Edit: 11/19/2013 10:39 PM by go4mars »
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Offline QuantumG

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Or something else efficient (and more plausible like a crane and click-in connections).

We shall call it "click and go" TSTO reusability. Spread the word.

*cough*LEGO*cough*
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline meekGee

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Or something else efficient (and more plausible like a crane and click-in connections).

We shall call it "click and go" TSTO reusability. Spread the word.

*cough*LEGO*cough*

Integration between first and second stage should be LEGO, no coughing.

It's just that no rocket to date has been designed this way.

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Offline StephenB

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This is getting a little fairies in the flame trench ish.

Offline rst

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Or first stage lands, someone throws an ablative tarp on top, second stage lands on the first.  Or something else efficient (and more plausible like a crane and click-in connections).

Land on top?  And if the second stage thrusters get wonky on landing, it potentially takes the first stage with it.

Besides, I would have thought that the time-consuming parts of setting up the stack would be managing the connections between the stages, and between both and the support structure (electrical and fuel lines, etc.).   The crane is a whole lot more plausible.

Offline meekGee

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Or first stage lands, someone throws an ablative tarp on top, second stage lands on the first.  Or something else efficient (and more plausible like a crane and click-in connections).

Land on top?  And if the second stage thrusters get wonky on landing, it potentially takes the first stage with it.

Besides, I would have thought that the time-consuming parts of setting up the stack would be managing the connections between the stages, and between both and the support structure (electrical and fuel lines, etc.).   The crane is a whole lot more plausible.

I'm sure the "land on top" comment was facetious.

However, with fully reusable components, there shouldn't be any connections between the stages.  The first stage should be a stand-alone flyer, no different than a carrier airplane".   This was never the case since expendable rockets need only one set of avionics, so the top of stack always drives the rocket.  But even with today's F9.1, the second stage has all the hardware necessary to do so. (and as far as I know, maybe it does).

In this case, the second stage only shadows before stage separation, but then becomes its own master at the moment of separation.

If you do that, the amount of communication necessary between the stages is minimal, and basically no electrical connection are necessary.

Connecting the two stages then is purely mechanical, and if you build a worthy latch system, that's all there is to it - "LEGO".

This kinda eliminates (or at least sharply reduces) one of SSTO's greatest selling points - the elimination of stage integration.

Payload integration, meanwhile, is pretty equivalent.


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Offline QuantumG

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If that were possible, I'd imagine the only other selling point of the SSTO would be the ability to land and relaunch from multiple launch sites. Aka, point to point. That'd be a minor advantage, though, as you could just have first stages at each launch site that return to their respective launch site after each launch.

Now, here's a thought: wouldn't it be nice to have one of these fully reusable TSTO first stages stationed at a base on Mars? Or the Moon.


I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline meekGee

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Exactly - in a point-to-point scenario, the first stages are bound to their respective airports, and the second stages travel the world.

Mathematically speaking, since for every upper stage that lands there is an upper stage that leaves shortly thereafter, (since the number of upper stages at any airport can't accumulate) then it's equivalent to the case where the first stage arrives with the upper stage and departs with it (aka single-stage suborbital plane).  (The continuity condition for imaginary spaceplanes!)

But all in all - I am not sure point-to-point is indeed a coming market - and I don't think it affects SpaceX designs.

I am pretty convinced that in Elon's mind, you don't have a "rocket that is shedding parts on ascent", but rather the first stage, complete with legs, avionics, etc, is just a carrier aircraft.  That's how come he's speaking in terms of hours per turn-around, and why SSTO is not a buzz word with him.   SSTO was commonly conceived as the anti-thesis for a traditional staging rocket - but it loses its allure in the face of two-component (not stage!) launch system.
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Offline guckyfan

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Now, here's a thought: wouldn't it be nice to have one of these fully reusable TSTO first stages stationed at a base on Mars? Or the Moon.

Actually, no. Gravity on Mars allows for SSTO and back. So no real need for a first stage.

Offline ArbitraryConstant

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Now, here's a thought: wouldn't it be nice to have one of these fully reusable TSTO first stages stationed at a base on Mars? Or the Moon.
Might the second stage might make more sense in either case? Delta-v from Mars surface to Mars orbit is similar to second stage delta-v to Earth orbit, and the surface pressure is near vac so vac optimized engines are fine.

Earth first stages solve a problem that basically only exists on Earth.

Offline meekGee

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Yes - SSTO on Mars makes sense, and seems to come out similar to a second stage.

Whether they'll be the same thing exactly - if I can get that knowledge for Christmas, I'll be a happy little boy.

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Offline QuantumG

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Yes - SSTO on Mars makes sense, and seems to come out similar to a second stage.

Whether they'll be the same thing exactly - if I can get that knowledge for Christmas, I'll be a happy little boy.

5 km/s sounds like a nice round number. It'll get you to the surface of Mars from LEO on a ~6 month trajectory and, after refueling, back to Earth again, while also giving you global planetary access.

I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline guckyfan

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Yes - SSTO on Mars makes sense, and seems to come out similar to a second stage.

Whether they'll be the same thing exactly - if I can get that knowledge for Christmas, I'll be a happy little boy.

They may be designed for Mars duty but they will very likely begin their life as a second stage of some vehicle launching from earth. IMHO of course.

Offline dante2308

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Superseded by more accurate calculations.
« Last Edit: 12/15/2013 03:45 PM by dante2308 »

Offline e of pi

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I did a little optimization on my launch trajectory.
*snip*
"Main engine cut off! The mass fraction is 0.0354212260744"
*snip*
It's a bit more feasible.
Except that I'm not aware of any rocket stage that has 3.5% burnout mass--and to get any payload at all, you'de need less than that. Your old version only required 4.6%, this requires more aggressive structure, not less. Elon says FH is supposed to have 1/30th (or about 3.3%) but even that unprecedented number would only leave about 0.16% of the gross liftoff weight as payload. That's less than 1.6 tons for this thousand ton monster, and it's got to be expendable to manage that.

Offline dante2308

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I did a little optimization on my launch trajectory.
*snip*
"Main engine cut off! The mass fraction is 0.0354212260744"
*snip*
It's a bit more feasible.
Except that I'm not aware of any rocket stage that has 3.5% burnout mass--and to get any payload at all, you'de need less than that. Your old version only required 4.6%, this requires more aggressive structure, not less. Elon says FH is supposed to have 1/30th (or about 3.3%) but even that unprecedented number would only leave about 0.16% of the gross liftoff weight as payload. That's less than 1.6 tons for this thousand ton monster, and it's got to be expendable to manage that.

Your calculation of 4.6% was wrong. Each engine is about 2.94 MN. (326/365)*5*2.94MN/(9.81+2.85) ~=  1,100,000 kg. The mass percent was under 2 last time. I don't think we're there yet, but there is a slight mass savings from having a single stage and no interstage. Also no separate upper stage engine (not a trivial weight mind you). I think 4% would be achievable. We'll see.

Edit: I just looked at what you wrote a bit more carefully. 3.542%-3.3% = 0.242% = 2.42 tons.
« Last Edit: 12/07/2013 10:42 PM by dante2308 »

Offline dante2308

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Just one more comment to my dead thread on SSTO. I've (nearly) perfected my orbit calculator. It will target a specified circular orbit and produce a lot of information. Barring bugs and computer numerical integration error, it will produce a lot of very accurate information based on many dynamic variables including:

Drag as a function of pressure, altitude, Mach number, temperature
Initial conditions as a function of Latitude and Longitude
Thrust as a function of a maximum g-load with respect to the available thrust envelope
Earth size and shape as a function of oblateness
Dynamic Isp changes as a function of atmospheric pressure and other variables

My first outputs were off due to a few bugs, poor trajectory optimization, and a large time step. My most recent results are much more accurate, but not perfect. However, they are accurate enough to answer some questions.

For those of us who don't have access to STK, I would be happy to calculate the performance of hypothetical rockets. Here is the most recent output for my program based on the question in the OP:

The lift off mass is 1000 tons
The initial acceleration is 3.25979758456 m/s^2
The initial thrust percent is 100
The initial number of engines cut off are 0 out of 5
Main engine cut off! The mass fraction is 0.0371414054242
The time is 316.76 seconds
Velocity is 7.8138971901 km/s
Altitude is 166.578020591 km
Altitude is 150.058766559 km (max Earth radius)
The final thrust percent is 70
The final number of engines cut off are 4 out of 5
Orbit Achieved!! Circular orbit velocity was 7.81376010016 km/s
Current mass is 37.1414054242 tons
The apogee (max Earth radius) is 154.235545544 km
The perigee (max Earth radius) is 147.93978061 km
The inclination is 28.5722681456 degrees

Attached is a sample local altitude versus time graph during the ascent.

To answer the question of SSTO for Raptor, you can get at least 3.7% of the take off mass into a 150kmx150kmX28.6 orbit as measured by the maximum radius of the Earth. The delta v back to the atmosphere from this orbit is not particularly onerous at 39.27m/s or a few hundred kg of fuel. It is not impossible, but it is an engineering nightmare. Much more useful would be calculations from the Martian surface.


Offline Avron

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Yes - SSTO on Mars makes sense, and seems to come out similar to a second stage.

Whether they'll be the same thing exactly - if I can get that knowledge for Christmas, I'll be a happy little boy.

5 km/s sounds like a nice round number. It'll get you to the surface of Mars from LEO on a ~6 month trajectory and, after refueling, back to Earth again, while also giving you global planetary access.



I think we are getting closer. Trying to find the factual comments from Elon and not what the reporters interpreted .. one is   I think you could land with the entire thing, said Musk (Royal Aeronautical Society ) he also noted -  "Probably not a Mars cycler; the thing with the cyclers is, you need a lot of them," Musk ( SPACE.com)

I was looking for where Elon mentions  Raptor in connection with a vehicle, and all I can find is "spaceship" (Royal Aeronautical Society ) . I cannot find Elon mention Raptor and launch vehicle in the same context.

What we do know is Elon wants the "spacecraft" back . and 'ship back because those things are expensive'

Offline meekGee

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I think we are getting closer. Trying to find the factual comments from Elon and not what the reporters interpreted .. one is   I think you could land with the entire thing, said Musk (Royal Aeronautical Society ) he also noted -  "Probably not a Mars cycler; the thing with the cyclers is, you need a lot of them," Musk ( SPACE.com)
That meshes well with the 3-month transit statement.
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Offline dante2308

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Yes - SSTO on Mars makes sense, and seems to come out similar to a second stage.

Whether they'll be the same thing exactly - if I can get that knowledge for Christmas, I'll be a happy little boy.

5 km/s sounds like a nice round number. It'll get you to the surface of Mars from LEO on a ~6 month trajectory and, after refueling, back to Earth again, while also giving you global planetary access.



I think we are getting closer. Trying to find the factual comments from Elon and not what the reporters interpreted .. one is   I think you could land with the entire thing, said Musk (Royal Aeronautical Society ) he also noted -  "Probably not a Mars cycler; the thing with the cyclers is, you need a lot of them," Musk ( SPACE.com)

I was looking for where Elon mentions  Raptor in connection with a vehicle, and all I can find is "spaceship" (Royal Aeronautical Society ) . I cannot find Elon mention Raptor and launch vehicle in the same context.

What we do know is Elon wants the "spacecraft" back . and 'ship back because those things are expensive'

Musk also stated that a cycler would have an inclination issue.

Offline dante2308

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Yes - SSTO on Mars makes sense, and seems to come out similar to a second stage.

Whether they'll be the same thing exactly - if I can get that knowledge for Christmas, I'll be a happy little boy.

Merry Christmas! Not only does SSTO work on Mars, you can escape Mars with more mass than a two stage rocket could put in LEO with the same lift-off mass.

The very same SSTO:

The lift off mass is 1000 tons
The initial acceleration is 43.6676675604 m/s^2
The initial thrust percent is 88
The initial number of engines cut off are 2 out of 6
Main Engine Cut OFF
The time is 123.085 seconds
Velocity is 4.98660320793 km/s
Altitude is 65.3562801306 km
Altitude is 49.9313317088 km (max Mars radius)
The final thrust percent is 70
The final number of engines cut off are 5 out of 6
Mars Escape!! Escape orbit velocity was 4.98601698629 km/s
Current mass is 124.7255312 tons

Major problem trying to get into LMO. You need some really deep throttle.

Quote
Design details of Falcon Heavy, and of Merlin 1D performance, have not been divulged.  In order to achieve the payload capability claimed by SpaceX, the new rocket engine will have to provide improved specific impulse and the stages will have to provide very high propellant mass ratios.  SpaceX claimed that the two "first stage" strap-on units will achieve a 30 to 1 gross mass to dry mass ratio, implying an unprecedented propellant mass fraction of better than 0.966

If one assumes that Elon landed 50 tons on Mars and 34 tons of that would need to be structural to get up to 1000 tons with the quoted fraction. Of course this is silly. You don't need anything that size.

Point is that SSTO works wonderfully on Mars. We should move there...

« Last Edit: 12/17/2013 02:28 AM by dante2308 »

Online Robotbeat

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If that were possible, I'd imagine the only other selling point of the SSTO would be the ability to land and relaunch from multiple launch sites. Aka, point to point. That'd be a minor advantage, though, as you could just have first stages at each launch site that return to their respective launch site after each launch.

Now, here's a thought: wouldn't it be nice to have one of these fully reusable TSTO first stages stationed at a base on Mars? Or the Moon.

Yeah, I'm not sure how comfortable I am with hand-waving away how difficult integrating two stages is, but I certainly think it's an /entirely/ plausible alternative to the much more technically difficult reusable SSTO problem. If there's a need for such rapid integration, it's certainly technically feasible.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

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