Author Topic: DARPA Experimental Spaceplane 1 (XS-1) Program  (Read 212005 times)

Offline envy887

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #760 on: 11/01/2017 12:56 PM »
Speculative. This isnít the most complex of programs and is entirely doable within the timeframe given by a company like Boeing and their experience in these areas.
Sure they do, so had Lockheed with the X33 and then we had Constellation and all the other "wonderful" projects of the past 30 years. All had cost and time overruns.
The problem is that the timeframe falls right into the ballpark time where a new administration would cancel it. Has happened before.
Personally, I am also underwhelmed by the concept, considering what SpaceX and Blue are doing right now. If this was an SSTO, it would be interesting but as it is, I am not at all excited.

One of the drawbacks of the SpaceX and Blue concepts is the low staging velocity dictating a large and expensive upper stage. I like the idea of faster staging and glideback allowing a smaller upper stage, although I think Boeing's implementation has about 0% chance of hitting the $5M cost and 1 day turnaround targets. LH2 and SSME were both terrible choices, IMO.

I would like to see what a similar all-methalox vehicle would look like, e.g. a single BE-4 booster and single Broadsword upper stage.

Offline whitelancer64

Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #761 on: 11/01/2017 01:02 PM »
I think Darpa wants to use mach10 capability for highspeed testing of other vehicles eg scamjet missiles.

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Keep in mind that Mach 10 is peak velocity at MECO, not speed in level flight.
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Offline Elmar Moelzer

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #762 on: 11/01/2017 02:55 PM »
One of the drawbacks of the SpaceX and Blue concepts is the low staging velocity dictating a large and expensive upper stage.
If the system was optimized for such a small payload, I am pretty sure the staging velocity could be higher (and the upper stage smaller). IIRC, a F9 first stage by itself is almost SSTO capable. So they should be able to do a Mach 10 MECO quite easily with such a small load on top and still have enough fuel for RTLS. I would assume that they could even remove a few Merlins from the first stage, but I may be wrong with that.

Offline john smith 19

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #763 on: 11/02/2017 10:01 AM »
If the system was optimized for such a small payload, I am pretty sure the staging velocity could be higher (and the upper stage smaller). IIRC, a F9 first stage by itself is almost SSTO capable. So they should be able to do a Mach 10 MECO quite easily with such a small load on top and still have enough fuel for RTLS. I would assume that they could even remove a few Merlins from the first stage, but I may be wrong with that.
Quite possibly.

The problem is not the going up. It's the coming down, as SX realized some years ago.
You're looking at something like 10x the KE and PE per Kg of mass from LEO that you are from their staging velocities and altitudes.

That's what's killed talk of a reusable F9 US. 
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Offline Elmar Moelzer

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #764 on: 11/02/2017 05:39 PM »
If the system was optimized for such a small payload, I am pretty sure the staging velocity could be higher (and the upper stage smaller). IIRC, a F9 first stage by itself is almost SSTO capable. So they should be able to do a Mach 10 MECO quite easily with such a small load on top and still have enough fuel for RTLS. I would assume that they could even remove a few Merlins from the first stage, but I may be wrong with that.
Quite possibly.

The problem is not the going up. It's the coming down, as SX realized some years ago.
You're looking at something like 10x the KE and PE per Kg of mass from LEO that you are from their staging velocities and altitudes.

That's what's killed talk of a reusable F9 US.
Was not saying that they should/ could do SSTO with the first stage, but they could certainly do Mach 10 for staging maybe still do an RTLS with such a small payload and second stage on top of it.

Offline envy887

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #765 on: 11/02/2017 06:50 PM »
If the system was optimized for such a small payload, I am pretty sure the staging velocity could be higher (and the upper stage smaller). IIRC, a F9 first stage by itself is almost SSTO capable. So they should be able to do a Mach 10 MECO quite easily with such a small load on top and still have enough fuel for RTLS. I would assume that they could even remove a few Merlins from the first stage, but I may be wrong with that.
Quite possibly.

The problem is not the going up. It's the coming down, as SX realized some years ago.
You're looking at something like 10x the KE and PE per Kg of mass from LEO that you are from their staging velocities and altitudes.

That's what's killed talk of a reusable F9 US.
Was not saying that they should/ could do SSTO with the first stage, but they could certainly do Mach 10 for staging maybe still do an RTLS with such a small payload and second stage on top of it.

I don't think it could. If you stage at 3,000 m/s, you need over 3,000 m/s just to null downrange velocity of the booster (while carrying entry and landing fuel). I get the F9 booster as having 3,300 m/s available at that point, which is not enough considering entry and landing need over 1,000 m/s. It's almost easier to just send the booster on into orbit than to RTLS from Mach 10.

XS-1 gets around this by using the atmosphere to slow down, turn around, and glide back empty. This should work if it flies a depressed trajectory, just exiting the atmosphere long enough for the upper stage to get to orbit. With a fairly thrusty upper stage (e.g. 35 klbf Broadsword), this takes ~130 seconds, during which time the booster will coast ~390 km downrange. This can be less if the upper stage eats some of the gravity losses.

Offline john smith 19

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #766 on: 11/02/2017 07:33 PM »

I don't think it could. If you stage at 3,000 m/s, you need over 3,000 m/s just to null downrange velocity of the booster (while carrying entry and landing fuel). I get the F9 booster as having 3,300 m/s available at that point, which is not enough considering entry and landing need over 1,000 m/s. It's almost easier to just send the booster on into orbit than to RTLS from Mach 10.

XS-1 gets around this by using the atmosphere to slow down, turn around, and glide back empty. This should work if it flies a depressed trajectory, just exiting the atmosphere long enough for the upper stage to get to orbit. With a fairly thrusty upper stage (e.g. 35 klbf Broadsword), this takes ~130 seconds, during which time the booster will coast ~390 km downrange. This can be less if the upper stage eats some of the gravity losses.
How tough this problem is depends on how long the design stays at M10 and at what altitude. It's a VTO so presumably it will be at less tahn 1/2 SL pressure by the time it breaks M1 and starts to go horizontal (or strictly speaking into a non-vertical climb).

With a fast enough climb and acceleration they could go with an ablative TPS and have minimal burn off.

Interesting small detail about the Ames TPS PICA and SIRCA. SIRCA can be mfg not only as rigid sections but also a stiff "spongy" like layer. This proved exceptionally handy for the back shell of the Curiosity rover aeroshell. This had lots of "closeouts" IE doors, panels, holes for cables. With rigid TPS you can put a panel on the door, but what about the area around it? The hinges? The frame?
Being flexible meant you could lay a layer over the door and then cut the outline of the door into it. Simple, fast and effective.

Control surfaces would probably be difficult but a sort of "glove" should work there.
« Last Edit: 11/02/2017 10:14 PM by john smith 19 »
"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 TrevorMonty

Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #767 on: 11/02/2017 10:05 PM »
I don't think M10 requirement was for normal orbital launches more for possible testing. Operational separation velocity is more likely to be in M5-10 region.


Offline Elmar Moelzer

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #768 on: 11/03/2017 02:36 AM »
Was not saying that they should/ could do SSTO with the first stage, but they could certainly do Mach 10 for staging maybe still do an RTLS with such a small payload and second stage on top of it.

I don't think it could. If you stage at 3,000 m/s, you need over 3,000 m/s just to null downrange velocity of the booster (while carrying entry and landing fuel). I get the F9 booster as having 3,300 m/s available at that point, which is not enough considering entry and landing need over 1,000 m/s. It's almost easier to just send the booster on into orbit than to RTLS from Mach 10.
The Falcon 9 1.1 first stage by itself has a DeltaV of at least 8300 m/s according to my calculations.
Of course, then you need to add the weight of an upper stage plus its fuel. Let's assume some 20 tons of mass for that (dry weight of a conservative 3,000 kg plus the payload of 1,000 kg and the rest is fuel).
With that I still get a Delta V of at least 7500 m/s and that is assuming it carries the fueled second stage all the way back too. So it would still have 1500 m/s for the rest.
Things may be looking even better with the latest versions of Falcon 9 and even more with block 5.
I might be wrong somewhere, but from this back of the envelope calculation, it still sounds plausible to me.

Offline su27k

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #769 on: 11/03/2017 03:03 AM »
I don't think it could. If you stage at 3,000 m/s, you need over 3,000 m/s just to null downrange velocity of the booster (while carrying entry and landing fuel). I get the F9 booster as having 3,300 m/s available at that point, which is not enough considering entry and landing need over 1,000 m/s. It's almost easier to just send the booster on into orbit than to RTLS from Mach 10.

XS-1 gets around this by using the atmosphere to slow down, turn around, and glide back empty. This should work if it flies a depressed trajectory, just exiting the atmosphere long enough for the upper stage to get to orbit. With a fairly thrusty upper stage (e.g. 35 klbf Broadsword), this takes ~130 seconds, during which time the booster will coast ~390 km downrange. This can be less if the upper stage eats some of the gravity losses.

We'll see if glideback can really do this, there're papers comparing glideback with boostback and flyback, pretty much every time the glideback staging speed is the lowest among the 3.

Offline envy887

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #770 on: 11/04/2017 01:44 AM »
Was not saying that they should/ could do SSTO with the first stage, but they could certainly do Mach 10 for staging maybe still do an RTLS with such a small payload and second stage on top of it.

I don't think it could. If you stage at 3,000 m/s, you need over 3,000 m/s just to null downrange velocity of the booster (while carrying entry and landing fuel). I get the F9 booster as having 3,300 m/s available at that point, which is not enough considering entry and landing need over 1,000 m/s. It's almost easier to just send the booster on into orbit than to RTLS from Mach 10.
The Falcon 9 1.1 first stage by itself has a DeltaV of at least 8300 m/s according to my calculations.
Of course, then you need to add the weight of an upper stage plus its fuel. Let's assume some 20 tons of mass for that (dry weight of a conservative 3,000 kg plus the payload of 1,000 kg and the rest is fuel).
With that I still get a Delta V of at least 7500 m/s and that is assuming it carries the fueled second stage all the way back too. So it would still have 1500 m/s for the rest.
Things may be looking even better with the latest versions of Falcon 9 and even more with block 5.
I might be wrong somewhere, but from this back of the envelope calculation, it still sounds plausible to me.

You appear to be missing gravity and drag losses on the first stage, which take all of that 1500 m/s and maybe a little more.

XS-1 is supposed to put 1,300 kg to SSO, so lets try to match that with F9 staging at 3,000 m/s. Orbital velocity is about 7750 m/s, and it gains nothing from rotation of the Earth, so the upper stage needs 4750 m/s. With a dry stage mass fraction of 10%, the upper stage, payload, and propellant are about 9 tonnes (varies slightly depending on the fuel choice, but not enough to matter here).

The F9 v1.2 booster is 27 tonnes dry and holds 436 tonnes of kerolox, and with the 9 t upper stage total GLOM is 471 tonnes and mass at MECO (~4600 m/s with drag and grav losses) is 101 tonnes. Mass after separation is 92 tonnes, and after boostback (3350 m/s) is 34 tonnes. The 7 tonnes of remaining fuel are enough for about 1/2 of the entry burn, so this won't work, although we're pretty close.

Offline Elmar Moelzer

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Re: DARPA Experimental Spaceplane 1 (XS-1) Program
« Reply #771 on: 11/05/2017 08:05 AM »
Was not saying that they should/ could do SSTO with the first stage, but they could certainly do Mach 10 for staging maybe still do an RTLS with such a small payload and second stage on top of it.

I don't think it could. If you stage at 3,000 m/s, you need over 3,000 m/s just to null downrange velocity of the booster (while carrying entry and landing fuel). I get the F9 booster as having 3,300 m/s available at that point, which is not enough considering entry and landing need over 1,000 m/s. It's almost easier to just send the booster on into orbit than to RTLS from Mach 10.
The Falcon 9 1.1 first stage by itself has a DeltaV of at least 8300 m/s according to my calculations.
Of course, then you need to add the weight of an upper stage plus its fuel. Let's assume some 20 tons of mass for that (dry weight of a conservative 3,000 kg plus the payload of 1,000 kg and the rest is fuel).
With that I still get a Delta V of at least 7500 m/s and that is assuming it carries the fueled second stage all the way back too. So it would still have 1500 m/s for the rest.
Things may be looking even better with the latest versions of Falcon 9 and even more with block 5.
I might be wrong somewhere, but from this back of the envelope calculation, it still sounds plausible to me.

You appear to be missing gravity and drag losses on the first stage, which take all of that 1500 m/s and maybe a little more.

XS-1 is supposed to put 1,300 kg to SSO, so lets try to match that with F9 staging at 3,000 m/s. Orbital velocity is about 7750 m/s, and it gains nothing from rotation of the Earth, so the upper stage needs 4750 m/s. With a dry stage mass fraction of 10%, the upper stage, payload, and propellant are about 9 tonnes (varies slightly depending on the fuel choice, but not enough to matter here).

The F9 v1.2 booster is 27 tonnes dry and holds 436 tonnes of kerolox, and with the 9 t upper stage total GLOM is 471 tonnes and mass at MECO (~4600 m/s with drag and grav losses) is 101 tonnes. Mass after separation is 92 tonnes, and after boostback (3350 m/s) is 34 tonnes. The 7 tonnes of remaining fuel are enough for about 1/2 of the entry burn, so this won't work, although we're pretty close.
I think that you are overemphasizing the effect of drag and gravity losses, as we are not going all the way to orbit (though from what I understand, the booster gets to handle most of that).
Koreasat was roughly Mach 8 at stage separation. Granted that landed downrange on an ASDS. But then this was carrying a much heavier (8 times as heavy according to your numbers) upper stage and payload than it would have to for XS1.
Also, lets not forget that these values are for 1.2 and not for Block 5. Also lets not forget that the Mach 10 is not required for routine operation but only has to be demonstrated. So, ever optimistic me, still thinks that it would work, though as you say, it may be cutting it close for Mach 10 separation. Though I am not sure whether the Mach 10 demo allows for downrange landing instead of RTLS. I might have missed it, but is there anything know about the contractual requirements for that?

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