Author Topic: DARPA ALASA  (Read 23071 times)

Offline jongoff

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DARPA ALASA
« on: 03/29/2014 03:45 AM »
I'm not sure if there's already a thread on ALASA, but here's an announcement about Boeing's concept that was selected for Phase 2 funding:

http://www.boeing.com/boeing/Features/2014/03/bds_darpa_contract_03_27_14.page

It's an interesting concept. It uses and F15 (so probably going to do a zoom climb before separation), and while it has two stages, there are only one set of engines, and they're on the upper stage--it looks like the first stage is just a drop tank.

With launch at high altitude and with a zoom climb, they can probably keep the rocket delta-V to orbit down in the ~8km/s range, and the engines can be nearly vacuum optimized without too much overexpansion at ignition. It would seem like the thrust two weight ratio once the first stage has burned out may be an issue, but maybe they're running the stages blow-down, or maybe the upper stage is just running at lower pressure?

Definitely a DARPA-weird concept, but I don't see anything about it that is technically infeasible. I hope they can make all the details work and make it to flight. I'm not very confident that Boeing can make this work at the price-point that they were hoping for ($1M/flt), but I think they've got a reasonable chance of at least making it work.

~Jon

Online Blackstar

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Re: DARPA ALASA
« Reply #1 on: 03/29/2014 11:12 AM »
ALASA

Online gosnold

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Re: DARPA ALASA
« Reply #2 on: 03/29/2014 01:40 PM »
Any idea about the kind of propellant used? Liquid would probably need to be pumped to the top of the rocket, but swapping from one solid motor compartment to another with the same nozzle seems complicated.

Online edkyle99

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Re: DARPA ALASA
« Reply #3 on: 03/29/2014 01:54 PM »
Boeing's press release says that the first two stages use the same engines, which doesn't rule out a third, or fourth, or more stages. 

Nice Skunk Works misdirection, too, after all of that early talk about dual hypersonic mini-B-70s, etc.  This idea looks simple by comparison, even elegant.  The only question is can it be pulled off in the real world?  Margins are tiny from the outset - in mass, yes, but especially in cost.

 - Ed Kyle
« Last Edit: 03/29/2014 02:15 PM by edkyle99 »

Offline Skyrocket

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Re: DARPA ALASA
« Reply #4 on: 03/29/2014 04:16 PM »
Another illustration by Boeing

Offline Proponent

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Re: DARPA ALASA
« Reply #5 on: 03/29/2014 05:46 PM »
Any idea about the kind of propellant used? Liquid would probably need to be pumped to the top of the rocket, but swapping from one solid motor compartment to another with the same nozzle seems complicated.

If you really wanted to use solids, maybe you could use the same trick as Orion's LAS:  essentially have the solids fire forward into a U-shaped duct.  Just thinking out loud.  I seems highly unlikely to me that anyone would actually want to do this.

If the propellant is liquid, it's going to have to be fed into the combustion chamber at high pressure anyway.  I wouldn't guess that pumping from a rearward location would be a huge deal.  If you had to pump it 2 m forward at 10 Gs acceleration, the hydrostatic head would be on the order of 2 atm.

Online hop

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Re: DARPA ALASA
« Reply #6 on: 03/29/2014 07:43 PM »
If you really wanted to use solids, maybe you could use the same trick as Orion's LAS:  essentially have the solids fire forward into a U-shaped duct.
Also other tractor type escape towers. However, since it has a drop tank we can rule out solids.

Quote
If you had to pump it 2 m forward at 10 Gs acceleration, the hydrostatic head would be on the order of 2 atm.
Since the same engines are used for the 1st and 2nd stage, it's a fair bet the first stage will be relatively low T/W.

Online RanulfC

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Re: DARPA ALASA
« Reply #7 on: 04/01/2014 02:51 PM »
Off-Topic note: Those engines are stolen from KSP! I recognize the "radial" engine set!

On-Topic: I thought I'd suggested such a set up before and seem to recall that I was told it wouldn't work "well" for an LV. I was under the impression that "tractor" rocket designs had some significant issues?

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline rusty

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Re: DARPA ALASA
« Reply #8 on: 04/04/2014 05:55 PM »
Another illustration by Boeing

I don't see how that can put 100lbs into orbit and considering how much even an AIM-120 costs, how they expect to do it for $1mil/flt. Article mentions a launch at 40,000ft (well below an F-15's ceiling) with the first two stages using common tractor engines. There's a lot missing here, including an adequate payload bay, so I can only conclude Boeing through Phantom Works got a chunk of cash to do some PR shots (like with the CST-100).
In that regard, this is a success as I've always dug the McDonnell Douglas F-15
« Last Edit: 04/04/2014 05:56 PM by rusty »

Online gosnold

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Re: DARPA ALASA
« Reply #9 on: 04/04/2014 06:58 PM »
Off-Topic note: Those engines are stolen from KSP! I recognize the "radial" engine set!

On-Topic: I thought I'd suggested such a set up before and seem to recall that I was told it wouldn't work "well" for an LV. I was under the impression that "tractor" rocket designs had some significant issues?

Randy

Well if you put them close to the fuselage you have to put them at an angle, which is less efficient (you have "cosine losses").
An interesting aspect of tractor configuration is that you can save mass on structural elements since you pull instead of pushing, so you don't have to worry about buckling.


Online RanulfC

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Re: DARPA ALASA
« Reply #10 on: 04/04/2014 07:52 PM »
I don't see how that can put 100lbs into orbit and considering how much even an AIM-120 costs, how they expect to do it for $1mil/flt. Article mentions a launch at 40,000ft (well below an F-15's ceiling) with the first two stages using common tractor engines. There's a lot missing here, including an adequate payload bay, so I can only conclude Boeing through Phantom Works got a chunk of cash to do some PR shots (like with the CST-100).
In that regard, this is a success as I've always dug the McDonnell Douglas F-15

At a "guess" (speculation mode engaged) I'd say that it would be a lot cheaper off the bat than an AIM-120 as the majority cost item for the AMRAAM is the seeker and control set. A pure "launch" guidence system is pretty inexpensive. The launch altitude is probably significant in that at 40,000ft in a near vertical climb the Eagle is still under acceleration so is providing more significantly towards the total Delta-V budget than if it launched at 80,000ft and almost no airspeed or engine thrust left, As for the payload bay I'm guessing it is actually the "nose-cone" and it's a fairing with engines below that. It looks to be skinner, but longer than the ASAT missile. (Speculation Mode disengaged)

Really they need to drop the F-15 and keep the engines :) A pair of jet-pods with F100s and enough fuel for the job would be about the size of a pair of cruise missiles and be able to stage the LV at over 80,000ft and Mach-2 while returning to land at the launch site.

Well if you put them close to the fuselage you have to put them at an angle, which is less efficient (you have "cosine losses").
An interesting aspect of tractor configuration is that you can save mass on structural elements since you pull instead of pushing, so you don't have to worry about buckling.

The cosine losses weren't what I seem to recall everyone talking about. I seem to recall that the exhaust impingment was considered a "serious" issue though I'm not sure why.

The main "advantage" aspect I was looking for at the time was putting the engines high above the surface for landing without sending debris all over at high velocity. I'd like to actually see more tractor concepts :)

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline Misha Vargas

Re: DARPA ALASA
« Reply #11 on: 04/05/2014 09:04 PM »
I know this design is not a staged design, but couldn't a tractor-style second stage have the ability to fire from the beginning of launch, reducing dead weight and lower the size of the first stage engines? Isn't this what the Shuttle was, in a sense? Also, if Boeing's design requires pumping fuel up from the drop tanks, could a staged design not pump fuel from the first stage into the second? (A sort of "vertical crossfeed".)

This has been floating around in my brain for a long time, and I can't figure out where (or if) I'm crazy.

Offline simonbp

Re: DARPA ALASA
« Reply #12 on: 04/06/2014 01:19 AM »
Are all four engines burning after it drops the drop tank? I hope the payloads are rated for 10+ g acceleration...

Offline jongoff

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Re: DARPA ALASA
« Reply #13 on: 04/06/2014 04:47 AM »
Are all four engines burning after it drops the drop tank? I hope the payloads are rated for 10+ g acceleration...

They may just drop the pressure a bunch for the upper stage. You'd need a good injector (pintle or swirler) to make it work, but if the first stage had a higher pressure and the upper stage has a lower pressure, you could keep the thrust levels reasonable.

~Jon

Offline simonbp

Re: DARPA ALASA
« Reply #14 on: 04/06/2014 05:44 PM »
Maybe, but the engines would need to throttle down a lot to keep the burn time long enough to end up with an orbit close to circular.

It would seem simpler if the first stage/zoom climb inject the vehicle on a pop-up trajectory, so after separation the second stage coasts to apogee and then does a quick, high-thrust circularization burn. It's killer for the payload, but really minimizes gravity losses. Plus, it would mean that you could launch to a range of inclinations from a single site and not have to worry about dropping stuff downrange.

ALASA is all about launching small recon/comm sats to LEO at strange inclinations, so that would seem to fit. I'm starting to understand why Boeing won.

Offline Zed_Noir

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Re: DARPA ALASA
« Reply #15 on: 04/07/2014 01:30 AM »
Can the 1st stage burn be pump-feed and the 2nd stage burn be pressure-fed? Presumably the pump gets discarded with the 1st stage. It would be something like the propellants gets pumped from the 1st stage tankage to the 2nd stage tankage to the combustion chambers for the 1st stage burn.

Offline Misha Vargas

Re: DARPA ALASA
« Reply #16 on: 04/07/2014 03:22 PM »
Can the 1st stage burn be pump-feed and the 2nd stage burn be pressure-fed? Presumably the pump gets discarded with the 1st stage. It would be something like the propellants gets pumped from the 1st stage tankage to the 2nd stage tankage to the combustion chambers for the 1st stage burn.

I'm not clear on terminology. By staging, you're referring to the Boeing proposal, not traditional staging (like I proposed a few posts back), right? Are drop tanks stages? Wiki says no, Boeing (or at least Steve Johnston) says yes...huh.

Offline simonbp

Re: DARPA ALASA
« Reply #17 on: 04/07/2014 09:43 PM »
That is one of those "how many angels can dance on the head of a pin" questions. A better question would be if any flown launch vehicle has used drop tanks on engines that continued to fire after the tank was dropped (unlike Shuttle). Old Atlas did the opposition (dropping booster engines while the sustainer continued to fire), but I can't think of any flown vehicles with drop tanks.

Usually you want to get rid of all the mass you can as quickly as you can. Boeing has to have some very good reason for keeping all four engines through second stage burnout.
« Last Edit: 04/07/2014 09:48 PM by simonbp »

Offline Skyrocket

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Re: DARPA ALASA
« Reply #18 on: 04/07/2014 10:36 PM »
but I can't think of any flown vehicles with drop tanks.

Proton-M Briz-M uses a drop tank on the Briz-M upperstage.

Offline francesco nicoli

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Re: DARPA ALASA
« Reply #19 on: 04/07/2014 11:10 PM »
just for the sake of curiosity: did you try it? :P

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