Author Topic: SSTO Thread  (Read 182217 times)

Offline HMXHMX

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Re: SSTO Thread
« Reply #560 on: 02/13/2009 05:16 am »
Airlaunch LLC are developing a 2-stage, air-launched, LOX/Propane rocket called the QuickReach. I'm not sure if it's sub-cooled propane. I suspect not since they use VAPAK, but I could easily be wrong.

http://www.airlaunchllc.com/index.htm

Thanks--that is interesting.  But now I am really confused.  This is, as you say, a propane-fueled vehicle.  It also uses VaPak propellant pressurization.  Gary Hudson is deeply involved.  But, on Selenian Boondocks Gary Hudson mentions that methane is better than propane for VaPak for operational reasons.  Perhaps AirLaunch recently switched from propane to methane and the information on the AirLaunch site is out of date?

I'll try to clarify.

AirLaunch traded propane and methane (LNG, actually) in 2003.  Performance defined as payload deployed was within 1% of each other; as many others have noted there is not much difference between the two propellants.   But we chose propane since it was non-cryogenic and we thought that would be beneficial with regard to pressure/temperature control while in the aircraft.  We already had to deal with a cryogen (LOX) and didn't want to complicate the issue. Finally, we thought that propane would be easier to obtain and store than LNG for the particular application.

After development and testing, however, what we found was LNG would make it much easier to control temp and pressure.  This turns out to be a universal truth: if one is using VaPak propellants, the operational temperature of the propellants should be well below ambient.  In propane's case, it might be necessary to cool it on a hot day or warm it on a cold day.  For a pure cryogen, it is only necessary to vent to control temperature.  In hindsight, this is perhaps obvious, but sometimes we can be denser than our propellants...

AirLaunch then demonstrated firing the same engine on LNG, and that works fine.  If Falcon has gone forward we would have argued for a change to LNG.  For purely space launch missions, if VaPak is the pressurization scheme, I would use LNG, especially for external-carriage air-launching.  But there are definitely vehicle concepts where propane is desirable in place of LNG; I leave discovery of those as an exercise for the interested.

Falcon SLV is cancelled then? I hadn't heard. What a shame.  Are you continuing to develop QuickReach? Seeking alternative funding?

QuickReach is mostly at CDR level but unless there is a new customer, it won't be built.  I'm open to doing something with it, but frankly won't spend a lot of effort seeking new funding.  The FALCON program had some very specific good points that attracted me in 2003, when "FALCON" became "Falcon"* and lost the strike mission, the rationale for continuing the program really disappeared.

(*no relation to SpaceX Falcon)

Offline HMXHMX

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Re: SSTO Thread
« Reply #561 on: 02/13/2009 05:21 am »
To be fair, a cryogenic fuel is a much bigger pain in the backside than a cryogenic oxidizer (and both John and some of my friends at XCOR agree).  GOX vapors can't burn in air--methane or propane vapors can.  While dealing with those issues isn't a show-stopper, it is a lot more of a hassle than dealing with LOX leaks.

This is all very interesting, and I think I've learned more from your posts and from HMXHMX's posts in this thread than just about any others I've ever read.

If I could ask a couple of other questions about sub-cooled propellants....

In practice how would one keep the propellant cool in a largish vehicle launched from the earth's surface?  From HMXHMX's posts about the AirLaunch Falcon, it sounds like insulation alone would probably not be sufficient  If cooling is needed, would it be done by circulating propellant or by building a refrigerator around the vehicle?  Or something else entirely...?

Secondly, is the large thermal expansion as a densified propellant warms up to the boiling point a major engineering issue?  I mean, if you're using a cryogen at its boiling point, then as long as your vents don't freeze shut, I would imagine that the worst that's likely to happen is that the tank boils dry.  But if I've got a tank of sub-cooled propane and cooling fails and I can't detank for some reason, do I have a time bomb on my hands?  Picture a tank of propane that's warming up and spurting liquid propane through its vents and may still burst.

EDIT: Corrected attribution of quote

AirLaunch's quickReach was not using sub-cooled propellants.  Just the opposite.  VaPak propellant are warmed to reach a particular desired vapor pressure, then maintained at the temperature until ignition.  But if one was using sub-cooled propellant, you'd just insulate appropriately.  No big deal.

Regarding your second question: just vent.  One always needs to size the vent to accommodate the gas flow that might result from the condition you describe. 

Offline space_man

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Re: SSTO Thread
« Reply #562 on: 04/09/2009 03:08 pm »
Great posts guys! I had a few ideas myself and just wanted to know what you think. As previously mentioned the key technologies necessary for SSTO are:

- lightweight structures
- hypersonic flight capability for airbreathing mode
- high specific impulse for rocket mode

I did some calculations and propose the following for an SSTO vehicle (possibly winged aircraft)

-Hybrid Engine with an airbreathing and a rocket mode. The airbreathing mode is capable of sustaining speed of Mach 4 and has a specific impulse of 2000sec. The rocket mode is based on tri-propellant combustion of flourine, berillium, and hydrogen and has a specific impulse of 700sec.

-Composite structure with a mass ratio of 2.5:1

Offline GI-Thruster

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Re: SSTO Thread
« Reply #563 on: 04/09/2009 05:58 pm »
Great posts guys! I had a few ideas myself and just wanted to know what you think. As previously mentioned the key technologies necessary for SSTO are:

- lightweight structures
- hypersonic flight capability for airbreathing mode
- high specific impulse for rocket mode

I did some calculations and propose the following for an SSTO vehicle (possibly winged aircraft)

-Hybrid Engine with an airbreathing and a rocket mode. The airbreathing mode is capable of sustaining speed of Mach 4 and has a specific impulse of 2000sec. The rocket mode is based on tri-propellant combustion of flourine, berillium, and hydrogen and has a specific impulse of 700sec.

-Composite structure with a mass ratio of 2.5:1


And who were you going to get to handle the Fluorine?  You'd need more than just one mother-in-law. . .

Offline MKremer

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Re: SSTO Thread
« Reply #564 on: 04/09/2009 06:17 pm »
Great posts guys! I had a few ideas myself and just wanted to know what you think. As previously mentioned the key technologies necessary for SSTO are:

- lightweight structures
- hypersonic flight capability for airbreathing mode
- high specific impulse for rocket mode

I did some calculations and propose the following for an SSTO vehicle (possibly winged aircraft)

-Hybrid Engine with an airbreathing and a rocket mode. The airbreathing mode is capable of sustaining speed of Mach 4 and has a specific impulse of 2000sec. The rocket mode is based on tri-propellant combustion of flourine, berillium, and hydrogen and has a specific impulse of 700sec.

-Composite structure with a mass ratio of 2.5:1


And who were you going to get to handle the Fluorine?  You'd need more than just one mother-in-law. . .

Also, what sorts of combustion byproducts would be generated? Not many people or governments would be very happy having tons of hydrofluoric acid dumped into the upper atmosphere with every launch.
 

Offline space_man

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Re: SSTO Thread
« Reply #565 on: 04/09/2009 06:23 pm »
Yes, I have read the thread on tri-propellants. I realize this generates tons of harmful chemicals, and the floruine is a nasty element to store.

But what about using regular propellants in the atmosphere and then engaging the tri-propellant engine in space where the pollutants would no longer be released into the actual atmosphere?

Offline clongton

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Re: SSTO Thread
« Reply #566 on: 04/09/2009 06:28 pm »
A better idea, once the nation finally gets over its mamby pamby fears, is to go nuclear. The exhaust is not radioactive. It’s practically impossible to make hydrogen radioactive, just very, very hot with lots of thrust and high isp.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline GI-Thruster

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Re: SSTO Thread
« Reply #567 on: 04/09/2009 06:29 pm »
Yes, I have read the thread on tri-propellants. I realize this generates tons of harmful chemicals, and the floruine is a nasty element to store.

But what about using regular propellants in the atmosphere and then engaging the tri-propellant engine in space where the pollutants would no longer be released into the actual atmosphere?

Well you can get more bang for your buck using these odd options but, you need to understand the practical reasons folks don't normally mess with Fluorine.  It's just a nightmare to deal with and that is never going to lead to a cost effective transport system.  We need to reduce support infrastructure in order to bring costs down, not create more infrastructure needs.

This is one of the reasons QR is such a good idea, the entire first stage is nothing like "rocket science."  It has the same safe, quick, convenient and economical advantages as all modern air transport.  Gary had basically a two stage rocket with the hassles of only a one stage rocket.  That was a VERY good idea.  I'm surprised that no one else wants to pick up that ball and run with it.  No one in Europe?  India? 

Just out of curiosity, if HMX is still around; I'd love to know why solids were passed over for QR.  That would have added a huge convenience to the entire concept.  Did solids just not have the get-up-and-go power you needed?

I'm also curious whether anyone ever considered the crazy option of carrying the rocket externally, pulling the plane up and releasing, then winging over the aircraft to get it away from the rocket quickly.  I know this sounds like a crazy stunt but in fact, B-47 pilots used to practice this maneuver to literally "throw" their payload at the target and get as far away as possible before the boom.  For anyone who has an interest, there's a DVD out there that describes this. I had occasion to view it myself since I picked it up for my father who crewed an RB-47 during the Korean conflict.  Very fun video and a little suprising to consider a bomber acting like a fighter.
« Last Edit: 04/09/2009 07:11 pm by GI-Thruster »

Offline space_man

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Re: SSTO Thread
« Reply #568 on: 04/09/2009 06:34 pm »
A better idea, once the nation finally gets over its mamby pamby fears, is to go nuclear. The exhaust is not radioactive. It’s practically impossible to make hydrogen radioactive, just very, very hot with lots of thrust and high isp.

I am curious, do you plan to pump hydrogen through exposed plutonium? (In which case temperature will be too high for modern nozzle materials)

Offline Jim

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Re: SSTO Thread
« Reply #569 on: 04/09/2009 07:36 pm »

But what about using regular propellants in the atmosphere and then engaging the tri-propellant engine in space where the pollutants would no longer be released into the actual atmosphere?

Still have to deal with them on the ground and then there is the accident scenario

Offline HMXHMX

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Re: SSTO Thread
« Reply #570 on: 04/10/2009 04:35 pm »
Yes, I have read the thread on tri-propellants. I realize this generates tons of harmful chemicals, and the floruine is a nasty element to store.

But what about using regular propellants in the atmosphere and then engaging the tri-propellant engine in space where the pollutants would no longer be released into the actual atmosphere?

Well you can get more bang for your buck using these odd options but, you need to understand the practical reasons folks don't normally mess with Fluorine.  It's just a nightmare to deal with and that is never going to lead to a cost effective transport system.  We need to reduce support infrastructure in order to bring costs down, not create more infrastructure needs.

This is one of the reasons QR is such a good idea, the entire first stage is nothing like "rocket science."  It has the same safe, quick, convenient and economical advantages as all modern air transport.  Gary had basically a two stage rocket with the hassles of only a one stage rocket.  That was a VERY good idea.  I'm surprised that no one else wants to pick up that ball and run with it.  No one in Europe?  India? 

Just out of curiosity, if HMX is still around; I'd love to know why solids were passed over for QR.  That would have added a huge convenience to the entire concept.  Did solids just not have the get-up-and-go power you needed?

I'm also curious whether anyone ever considered the crazy option of carrying the rocket externally, pulling the plane up and releasing, then winging over the aircraft to get it away from the rocket quickly.  I know this sounds like a crazy stunt but in fact, B-47 pilots used to practice this maneuver to literally "throw" their payload at the target and get as far away as possible before the boom.  For anyone who has an interest, there's a DVD out there that describes this. I had occasion to view it myself since I picked it up for my father who crewed an RB-47 during the Korean conflict.  Very fun video and a little suprising to consider a bomber acting like a fighter.

We traded out solids because of the DARPA/USAF cost target.  No way to get to to the target being captive to essentially only one manufacturer.  You also need three or more stages, adding to the overall cost. Since each stage is about as expensive as another, irrespective of size.

I have heard of a number of non-U.S. air-launch studies and programs.  I expect the idea is not dead.

We did look at external carriage, but there were reasons (that I can't get into) for the choices we made for FALCON.  t/Space did use external carriage and AirLaunch was assigned a patent on specifics of that approach last fall.  I'm fairly familiar with the B-47 maneuver you mention and in fact, I know of at least one air-launch concept that used it as the starting point for analysis.  It's hard on heavier vehicles and airframes, however.

By the way, getting the airplane away quickly is really only a problem for solids (that can detonate) versus airborne liquids that can really only deflagrate.  In flight, there is not a mechanism for propellants to mix (witness Challenger).



Offline mmeijeri

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Re: SSTO Thread
« Reply #571 on: 05/28/2009 01:34 am »
Hmmm, if ethane isn't too hard to produce from methane, then that's another Martian fuel choice. It has somewhat better handling properties and density for a touch less isp. And of course, from ethane you can make ethylene, base stock for the plastics industry.

You can make higher hydrocarbons, even diesel, from methane, see

Gas to liquids
What is Gas to Liquids?

I don't know how well this process could be adapted to Martian ISRU, if at all. Next time I bump into some old colleagues, I'll ask them.
« Last Edit: 05/28/2009 01:48 am by mmeijeri »
Pro-tip: you don't have to be a jerk if someone doesn't agree with your theories

Offline Proponent

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Re: SSTO Thread
« Reply #572 on: 07/14/2015 02:40 pm »
Having a little spare time during the summer lull, I've had a quick look at the effect of variable mixture ratios on lox-hydrogen SSTO.

I began by reproducing Dunn's results for 1000-m3 SSTO.  In Dunn's approximation, finding the payload to LEO is simply a matter of finding the burn-out mass that yields an ideal delta-V of 9500 m/s and then subtracting 20,000 kg plus 3% of the propellant load (that's for hydrogen; for other fuels he uses 25,000 kg and 2%).  Like Dunn, I use 90% of the vacuum Isp for the given mixture ratio, though my Isp figures come from RPA Lite 1.2.8.0 rather than from ProPEP.  As the table below shows, my payload figure for the mixture ratio of 6 that he asumed is similar to his (9350 kg).

Scenario      MR   Payload
            (mean)    (kg)
Max Isp      5.281    7389
Dunn         6.000    9333
Opt Fixed    7.622   11488
Variable     7.719   11873
Stoich       7.937   11270
Max Impulse 17.192  -12427

The table gives us a reminder that maximizing performance is not the same thing as maximizing Isp, as people so often assume.  Even Dunn's unusually-lean mixture ratio turns out to have been too low: bumping the MR all the way up to 7.6 adds more than 20% to the payload.

I then divide the 1000-m3 propellant volume into 100 equal slices, each of which consists of liquid oxygen and hydrogen in an arbitrary ratio.  I numerically adjust the mixture ratio in each slice to maximize the payload to orbit.  The resulting MR profile is a shown in the attached figure.  The mean MR of 7.7 is what is reported in the table, above.  The horizontal line in fhe figure shows the MR for the optimal fixed-MR case.

Frankly I'm disappointed that the variable MR appears to boost the payload by just a few percent over the optimal fixed-MR case.  I do suspect, though, that the benefit of variable-MR is understated, because the oxygen-rich mixture burned at lift-off would produce high thrust, thus reducing gravity losses.  (On the other hand, there's the complexity of building an engine which can handle a large range of MRs -- that's well beyond the scope of this simple calculation).

It must be the case in principle that right at lift-off, the optimal MR is that which maximizes the density impulse (density times Isp).  The reason is that the initial infinitesimal volume of propellant does not need to be accelerated of lifted off the pad, so the volume it occupies in the tanks might as well be packed as full of impulse as possible*.  I presume the fact that the present calculation does not show the MR rising that high at lift-off is that the optimal MR falls very quickly to lower values.



* Steven Pietrobon previously used this argument in approximate form to show that density impulse is relatively more important for first stages.  Here I'm using it in exact form for an infinitesimal first stage.

EDIT: Added a parenthetical about Dunn's assumptions for non-hydrogen fuels and fixed typos.  Expanded description of the figures and on argument about the density impulse for the initial slug of propellant.  Corrected parenthetical description of Dunn's mass model in the second sentence.
« Last Edit: 01/20/2017 12:49 pm by Proponent »

Offline john smith 19

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Re: SSTO Thread
« Reply #573 on: 07/15/2015 09:03 am »
Having a little spare time during the summer lull, I've had a quick look at the effect of variable mixture ratios on lox-hydrogen SSTO.
This technique has been applied.

It was written up in a paper by Logsdon & Africano on improving payload to the Moon with the Saturn V, along with several other techniques.

Variable MR was estimated to be responsible for 1/2 of the 5% improvement in payload to lunar orbit and needed no hardware changes, just valve settings to the J2. They describe it as a "gear change," a move from 1 valve setting to another, not a gradual sweep.
Quote
Frankly I'm disappointed that the variable MR appears to boost the payload by just a few percent over the optimal fixed-MR case.  I do suspect, though, that the benefit of variable-MR is understated, because the oxygen-rich mixture burned at lift-off would produce high thrust, thus reducing gravity losses.  (On the other hand, there's the complexity of building an engine which can handle a large range of MRs -- that's well beyond the scope of this simple calculation).
This was L&A's point. The lower Isp dumps more of the heavier O2 molecules lower in the trajectory, so the vehicle accelerates faster. BTW they noted that in the early 70's the cost per unit mass of payload to the Moon was more than the equivalent mass of Gold.

A 2.5% improvement is pretty good.
Quote
It must be the case in principle that right at lift-off, the optimal MR is that which maximizes the density impulse (density times Isp).  The reason is that the initial infinitesimal volume of propellant does not need to be accelerated of lifted off the pad, so the volume it occupies in the tanks might as well be packed as full of impulse as possible*.  I presume the fact that the present calculation does not show the MR rising that high at lift-off is that the optimal MR falls very quickly to lower values.
By extension there is an optimal MR for every point on the trajectory that maximizes a particular parameter, depending on what parameter that is.

Sadly they were not able to apply the technique to the Saturn V 1st stage.

In an atmosphere the trades are different. You want to get the engine nozzles to the design altitude fast, OTOH your peak dynamic pressure rises the lower in the atmosphere you are when you hit M1, so you don't want to accelerate too fast
« Last Edit: 07/15/2015 09:04 am by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline hkultala

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Re: SSTO Thread
« Reply #574 on: 07/16/2015 11:47 am »
Yes, I have read the thread on tri-propellants. I realize this generates tons of harmful chemicals, and the floruine is a nasty element to store.

But what about using regular propellants in the atmosphere and then engaging the tri-propellant engine in space where the pollutants would no longer be released into the actual atmosphere?

Practically all the exhaust you use to reach orbit will reach atmosphere. It will have much less velocity than the orbital velocity, as you are shooting it backwards.

Offline docmordrid

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Re: SSTO Thread
« Reply #575 on: 07/18/2015 08:57 am »
Interesting....we'll see.

Escape Dynamics beamed power SSTO

http://escapedynamics.com/edispacelaunch/
DM

Offline Asteroza

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Re: SSTO Thread
« Reply #576 on: 07/20/2015 03:55 am »
Escape Dynamics seems to have a press release for an end-to-end demo of a 100KW microwave beamed power thermal rocket, which is a step up beyond the demos done by Parker. Good to see some of the beamed power thermal thruster work progressing.

The other major beamed power groups have gotten quiet though. Lasermotive certainly hasn't been saying very much as of late.

Offline Devilstower

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Re: SSTO Thread
« Reply #577 on: 07/20/2015 03:52 pm »
Short article on Escape Dynamics announcement in popular press. Includes embedded video.

http://www.engadget.com/2015/07/20/escape-dynamics-microwave-spacecraft/
« Last Edit: 07/20/2015 03:53 pm by Devilstower »

Offline A_M_Swallow

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Re: SSTO Thread
« Reply #578 on: 07/20/2015 04:09 pm »
Short article on Escape Dynamics announcement in popular press. Includes embedded video.

http://www.engadget.com/2015/07/20/escape-dynamics-microwave-spacecraft/

If building microwave transmitters throughout the world is too difficult politically what is this system like as a first stage?

Offline Devilstower

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Re: SSTO Thread
« Reply #579 on: 07/20/2015 06:28 pm »
Personally, I'd go with an equator-girdling series of barge-mounted Masers over broad arrays of more conventional focused microwave sources on land. It's a daunting project either way, but pocket change compared to many suggestions for delivering material to orbit.

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