DARPA selects Boeing to work on XS-1

[DerekL1963]

11 hours ago, Nothalogh said:

But the better question is what exact natsec launch capability does this design service?

A polar orbit (as specified in the article and the requirements) is very useful for various kinds of surveillance birds.  Fast turnaround allowing the launch of many payloads (as specified in the article and the requirements) is very useful in the event of hostile action against orbital assets.

[insert_name]

engine has been test fired, the LOX tank is under construction http://spacenews.com/engine-tests-underway-for-darpa-spaceplane-program/

[linuxgurugamer]

On 5/24/2017 at 10:25 PM, Matuchkin said:

I'm getting reminded of the high hopes that most scrapped X-plane programs had. Hopefully they succeed, finally.

What are you talking about? By definition, an X plane is experimental, for research only.  And many have been quite successful

Edited July 5, 2018 by linuxgurugamer

[Racescort666]

So I started going down the rabbit hole on this one... Here's what I've got so far:

• Main engine: SSME "derivative" (per AR, it is literally an RS-25 with a new controller. aka, ECU swap in the aftermarket auto world, here)
  • Engine thrust: 1669 kN: here
  • Engine mass: 3527 kg: here
  • Engine ISP: 452 s (same source as above)
• The Booster: (for the purpose of this discussion, "the booster" is the space plane bit and I'll be referring to the upper stage as a separate entity.)
  • Length: 30.5 m here
  • Diameter: 4.1 (same source as above)
  • Wing span: 19 m (same source as above)
• Launch mass: ~131t based on a 1.3 TWR which is on par with Falcon 9 and Atlas V which are my typical yard stick. (Full estimate range is 162t-113t for 1.05-1.5 TWR)
• Upper Stage: (further discussion below) this is based on an RL10 powered upper stage with similar areal dry mass based on the Space Shuttle ET for a conservative estimate.
  • RL10 Mass: 168 kg (previous analysis)
  • RL10 ISP: 451 s (previous analysis)
  • Upper Stage Length: 9.8 m (scaled from rendering) 
  • Upper Stage Diameter: 2.3 m (scaled from rendering)
  • Note: upper stage volume is less than a Centaur upper stage, payload is considerably less than a typical Centaur for LEO, therefore TWR was not analyzed.
  • Upper Stage dV 7000 m/s (actual estimate 7624 m/s but in the name of being conservative, I chopped a bunch off)
• Estimated dry mass of booster: 60 000 kg

Further discussion: 
 

Spoiler

 

Unsurprisingly, there is very little information about this vehicle since it's a defense project. Boeing seems very interested in it though; and to be honest, they're probably the best contractor for the job. They are partially vested in the project, despite not disclosing how much money they had contributed toward it: Source. Regardless, Boeing built the X-37 and there's a good chance that the parts of Rockwell that they acquired include the IP related to building other historical spaceplanes like the Space Shuttle and the X-15 (Which were built by North American Aviation, which became North American Rockwell, Bob's your uncle, Boeing is the best at spaceplanes).  Purely speculation of course, but if I was a betting man...

Next, for hard numbers, all I have go on are the renderings. Are they accurate? I have no idea but since prototypes/ground tests/flight tests are to be conducted by 2020, the renderings may not be a terrible source. The numbers on the Boeing website suggest that they have decided on a basic envelope and that reinforces the fact that the renderings are good enough for a ballpark.

Without going too far into the weeds: my assumption is that this vehicle is intended for rapid replacement of existing hardware. i.e. hypothetically there was a military strike against existing in-space infrastructure and that infrastructure needs to be replaced ASAP. DARPA, being the agency it is, wants a tech demonstrator using mostly existing launch hardware that can demonstrate this capability (Kerbal IRL). So, assuming that there exists a satellite that has the capability of short term replacement of current communication/observation, the objective of this project is to launch 10 of these satellites over the course of 10 days.

The upper stage threw me for a loop at first until I started doing the math on alternatives. Initially, I figured that the upper stage would be a solid rocket since I figured it would be the best for quick turnaround. Also, it had the same form factor as some existing solid upper stages like the Orion 50 (Pegasus rocket for reference) in the renderings. Once I did the measurements from the video rendering, it was much larger than an Orion 50. It's basically the same diameter as a Castor motor... hmmm... the Castor 30 is used on the Antares rocket but Antares has got a much bigger payload capacity. ...running the numbers... whoa, Castor is way overpowered for this application. Plus, a Castor 120 would be size representative and would be almost half of the take off weight. There was no way that could be right. Educated guess: something powered by an existing engine that's fairly low thrust: enter, RL10. 

It's probably not a huge stretch to assume that an RL10 would be considered for this role if it weren't for the absurd cost of them. 1 RL10 is a significant portion of the DARPA contribution to this project. However, we don't know the cost of the current/future RL10 3D-printed model and AR is involved on this project as the engine supplier. Anyway, if the booster is HydroLox, why not the upper stage as well?

Further comments on dV for the upper stage: this dV is plenty to get to orbit since a Falcon 9 upper stage has about the same dV with a 10t payload. Atlas V is a different story but flies a different flight profile.

Edit: I assume this thing will fly an RTLS type flight profile which is why I consider the Falcon 9 to be an appropriate analogue for dV.

Thoughts on the dry mass: I don't have a good basis for comparison since nothing comparable has flown before. There are aspects of it that I haven't investigated but I didn't want to fall too deep down the rabbit hole. However, 60t and the length are approximately the size of a Gulfstream G550, even if the wingspan is a bit smaller which is to be expected.

 

Sorry about getting lazy about citing sources toward the end, most of it was from the 3 press releases and wikipedia. 

Edited July 6, 2018 by Racescort666

[Matuchkin]

On 7/4/2018 at 6:04 PM, linuxgurugamer said:

What are you talking about? By definition, an X plane is experimental, for research only.  And many have been quite successful

That comment was made a long time ago. I was more... stupid... back then.

[TheSaint]

Interesting project. DARPA has a very impressive (sometimes unnerving) track record of taking concepts that people describe as "impossible" and actually making them happen. That said:

"Advanced, lightweight composite cryogenic propellant tanks to hold liquid oxygen and liquid hydrogen propellants"

This is what wound up scuttling the X-33. If nothing else comes out of this program but a viable composite liquid hydrogen tank it will be worth every penny.

[mikegarrison]

5 minutes ago, TheSaint said:

Interesting project. DARPA has a very impressive (sometimes unnerving) track record of taking concepts that people describe as "impossible" and actually making them happen. That said:

"Advanced, lightweight composite cryogenic propellant tanks to hold liquid oxygen and liquid hydrogen propellants"

This is what wound up scuttling the X-33. If nothing else comes out of this program but a viable composite liquid hydrogen tank it will be worth every penny.

I think the industry in general (and Boeing in particular) has learned a lot about composites in the last 20 years.

[insert_name]

AR-22 test firings complete, managed to reduce turnaround on the engine to 17 hours

http://spacenews.com/darpa-companies-declare-success-in-ar-22-engine-test-series/

Edited July 11, 2018 by insert_name

[Racescort666]

17 minutes ago, insert_name said:

AR-22 test firings complete, managed to reduce turnaround on the engine to 17 hours

http://spacenews.com/darpa-companies-declare-success-in-ar-22-engine-test-series/

I wonder how much different the actual flights will be compared to the test stand. You hypothetically don't have any atmosphere at shutdown but you also have to deal with reentry. Reentry should be much more mild than the shuttle reentry though. 

[Wjolcz]

21 hours ago, TheSaint said:

Interesting project. DARPA has a very impressive (sometimes unnerving) track record of taking concepts that people describe as "impossible" and actually making them happen. That said:

"Advanced, lightweight composite cryogenic propellant tanks to hold liquid oxygen and liquid hydrogen propellants"

This is what wound up scuttling the X-33. If nothing else comes out of this program but a viable composite liquid hydrogen tank it will be worth every penny.

Not to derail this thread but I feel like the fuel tank issue was never solved because there never was a need for a cheap launcher like X-33. Now that the launch prices get lower and boosters are landing they will be more likely to spend a little more time and money on making sure the fuel tank works. And, yeah, composites have been around for a while now so the infrastructure shouldn't be too much of a problem.

[StrandedonEarth]

On 7/10/2018 at 6:54 PM, TheSaint said:

 

This is what wound up scuttling the X-33. If nothing else comes out of this program but a viable composite liquid hydrogen tank it will be worth every penny.

The problem with X-33’s composite hydrogen tank arose from the complex lobed shape. Although I don’t know if anyone has tried making a regular, cylindrical hydrogen tank...

[Xd the great]

On 7/12/2018 at 11:15 AM, StrandedonEarth said:

The problem with X-33’s composite hydrogen tank arose from the complex lobed shape. Although I don’t know if anyone has tried making a regular, cylindrical hydrogen tank...

Dude, just use aluminium. Problem solved.

[Toonu]

Just an idea. If the carrier plane will be specialized to launch it from some place to not affect its own flight path, would it be possible to take fuel from the plane itself to speed rocket and plane together before launch and flying with own fuel? I know the plane would need to be able to handle supersonic speeds but we had such planes for long time.

[Xd the great]

15 minutes ago, Toonu said:

Just an idea. If the carrier plane will be specialized to launch it from some place to not affect its own flight path, would it be possible to take fuel from the plane itself to speed rocket and plane together before launch and flying with own fuel? I know the plane would need to be able to handle supersonic speeds but we had such planes for long time.

The plane is designed to handle supersonic speeds. Its the attachment, the heat shields and the fuel the is hard.

[magnemoe]

4 hours ago, Xd the great said:

Dude, just use aluminium. Problem solved.

Yes that would work, however not in an SSTO.
First tips in making an successful launch vehicle is not making it an SSTO since its very hard. 
An good chance venturestar would end as an shuttle like hangar queen if build simply as you had to push all margins to the limits 

[Xd the great]

Aluminium is actually lighter in the x33 case.

2 hours ago, magnemoe said:

Yes that would work, however not in an SSTO.
First tips in making an successful launch vehicle is not making it an SSTO since its very hard. 
An good chance venturestar would end as an shuttle like hangar queen if build simply as you had to push all margins to the limits 

SSTO would be very large and heavy.

Has anyone used equations to show that a SSTO is next to impossible?

[magnemoe]

2 minutes ago, Xd the great said:

Aluminium is actually lighter in the x33 case.

SSTO would be very large and heavy.

Has anyone used equations to show that a SSTO is next to impossible?

SSTO is possible many first stages would be an SSTO with just an nose cap. Problem is that you need reuse for it to make sense. You are after all building an large, very advanced and expensive vehicle.
And dual stage with full reuse would be much easier since only the small upper stage goes into orbit and has to reenter. 
In short its probably possible but very unpractical 

[Exoscientist]

On 7/11/2018 at 11:15 PM, StrandedonEarth said:

The problem with X-33’s composite hydrogen tank arose from the complex lobed shape. Although I don’t know if anyone has tried making a regular, cylindrical hydrogen tank...

 Correct about the complex shape being the problem. Actually, cylindrical carbon composite tanks were well understood even then. That’s what led Lockheed engineers to think they could solve the case of conformal, i.e., following the shape of the aircraft, tanks. Unfortunately, it turned out with carbon composites the weight turned out worse than metal tanks rather than saving weight.
 However, recent high strength metal alloys are even more weight saving than carbon composites. This means we can now build the X-33 with even better than the original expected performance and build the VentureStar with even better than the originally expected payload as an SSTO:

DARPA’s Spaceplane:an X-33 version, Page 2.

https://exoscientist.blogspot.com/2018/06/darpas-spaceplane-x-33-version-page-2.html

  Bob Clark

 

 

[Exoscientist]

4 minutes ago, magnemoe said:

SSTO is possible many first stages would be an SSTO with just an nose cap. Problem is that you need reuse for it to make sense. You are after all building an large, very advanced and expensive vehicle.
And dual stage with full reuse would be much easier since only the small upper stage goes into orbit and has to reenter. 
In short its probably possible but very unpractical 

 We now know that even reusability of a two-stage vehicle (TSTO) costs significantly in payload. For instance, the Falcon 9 loses 30% of it’s payload with first stage only reuse and 40% payload is lost with full reuse.

 Since the SSTO doesn’t have the expense of an upper stage, there really has to be an accurate reassessment which comes out ahead on a cost per kilo basis. I emphasize cost per kilo because even though the TSTO will carry more payload it will lose more payload on reusability and cost more because of the upper stage.

  Bob Clark

[Xd the great]

Well, payload is significant for Mars rovers. Still, SSTOs are good for cheap cubesats.

[mikegarrison]

1 hour ago, Exoscientist said:

 Correct about the complex shape being the problem. Actually, cylindrical carbon composite tanks were well understood even then. That’s what led Lockheed engineers to think they could solve the case of conformal, i.e., following the shape of the aircraft, tanks. Unfortunately, it turned out with carbon composites the weight turned out worse than metal tanks rather than saving weight.
 However, recent high strength metal alloys are even more weight saving than carbon composites. This means we can now build the X-33 with even better than the original expected performance and build the VentureStar with even better than the originally expected payload as an SSTO:

DARPA’s Spaceplane:an X-33 version, Page 2.

https://exoscientist.blogspot.com/2018/06/darpas-spaceplane-x-33-version-page-2.html

  Bob Clark

 

 

I'll just point out that I was shooting arrows made from 7075 T6 alloy in 1990. https://eastonarchery.com/target/xx75-tribute-shaft/ These alloys you are talking about are not new and were not unknown to the X-33 designers.

Treating the composite as "black aluminum" is not good composite engineering. You can make composites that simulate an isotropic material like aluminum, but it's much better design to only make the composites strong in the directions they need to be strong. That makes it awfully hard to compare aluminum and composite just by looking at a single value of strength-to-weight.

Edited July 14, 2018 by mikegarrison

[Racescort666]

56 minutes ago, mikegarrison said:

Treating the composite as "black aluminum" is not good composite engineering. You can make composites that simulate an isotropic material like aluminum, but it's much better design to only make the composites strong in the directions they need to be strong. That makes it awfully hard to compare aluminum and composite just by looking at a single value of strength-to-weight.

Much easier said than done but even in the last 10 years our tools for analyzing and designing composites have improved significantly. It usually takes a very involved effort to refine and optimize a design. However, this can be helped by optimizer software which, again, has gotten better in recent years. A good composite design is no small task.

[magnemoe]

2 hours ago, Exoscientist said:

 We now know that even reusability of a two-stage vehicle (TSTO) costs significantly in payload. For instance, the Falcon 9 loses 30% of it’s payload with first stage only reuse and 40% payload is lost with full reuse.

 Since the SSTO doesn’t have the expense of an upper stage, there really has to be an accurate reassessment which comes out ahead on a cost per kilo basis. I emphasize cost per kilo because even though the TSTO will carry more payload it will lose more payload on reusability and cost more because of the upper stage.

  Bob Clark

No an SSTO don't have an upper stage so it need to carry all its dry mass up into orbit and then land it. Take falcon 9, first stage has an 25 ton dry mass second stage is 4 ton.
Even if you did not add weight on first stage for ssto you still had to put an 25 ton mass into orbit cutting directly into your payload, next you has to deorbit and land it. 
Nintendo hard, and even if it work you are probably only able to launch small satellites from an huge expensive vehicle.

On the other hand I assume you could reuse second stage with an 3-4 ton weight, extra fuel, heat shields additional RSC and other systems like parachutes, that is still an 70-100% penalty but you can accept is as the second stage is so light. the light weight also make it easier to recover. 
In short pretty sure some can prove mathematically that an TSTO will always win. 

This is true for all rocket engines, SSTO has the benefit of not having to integrate stages. Some future technology like Sabre , scamjet, laser or microwave heated engines might make SSTO comeptive however for Skylon you would still get more payload going suborbital and using an upper stage as you are only airbreathing up to mach 5. 

[Exoscientist]

On 7/14/2018 at 10:05 AM, mikegarrison said:

I'll just point out that I was shooting arrows made from 7075 T6 alloy in 1990. https://eastonarchery.com/target/xx75-tribute-shaft/ These alloys you are talking about are not new and were not unknown to the X-33 designers.

Treating the composite as "black aluminum" is not good composite engineering. You can make composites that simulate an isotropic material like aluminum, but it's much better design to only make the composites strong in the directions they need to be strong. That makes it awfully hard to compare aluminum and composite just by looking at a single value of strength-to-weight.

 Didn't know the 7075 was known that long. The X-33 engineers did try replacing the carbon composite with aluminum-lithium, so perhaps the advantage of 7075 over aluminum-lithium was not sufficient to justify its expense. Note though there are now alloys significantly stronger than 7075 as well.

 

 Bob Clark

[mikegarrison]

7075 actually dates back to WW2. It was a military secret of Imperial Japan. T6 refers to how the alloy is tempered.

Back when I first started archery, 7075 arrows were the top of the line. Cheaper arrows were made out of 60-series aluminum. These days 7075 is the bargain arrow, and more expensive arrows are either carbon fiber or carbon fiber bonded to aluminum.