Community > Forum > Technology & Science > Jet engines as boosters

Jet engines as boosters

Posted by: JamesHughes - Wed Feb 10, 2010 9:48 am
Post new topic Reply to topic
 [ 24 posts ] 
Jet engines as boosters 
Author Message
Space Station Commander
Space Station Commander
User avatar
Joined: Wed Aug 18, 2004 8:47 am
Posts: 521
Location: Science Park, Cambridge, UK
Post Jet engines as boosters   Posted on: Wed Feb 10, 2010 9:48 am
Was just thinking, would strapping on jet engines to a vertical rocket mean less fuel was required overall to get to orbit?

Lets say you strap 8 jet engines around the first stage. They would need to be supersonic capable of course, but lets say they run out of ability at mach 4.

The Ares-1 first stage was intended to run to mach 4.8 at 130kft, which I assume would be too high for a jet to be efficient.

Now, you could be the hybrid engine suggested by reaction engines which would keep running at these greater heights.....

Just a thought - where are the issues I have missed!


Back to top
Profile
Moderator
Moderator
avatar
Joined: Mon Feb 09, 2004 4:01 am
Posts: 747
Location: New Zealand
Post Re: Jet engines as boosters   Posted on: Wed Feb 10, 2010 10:53 am
Normally you skip to ramjets at around mach 2-3. Ten possibly to an oxidizer later in a pure rocket engine.

Turbines are just really heavy and hardly used except for HTHL craft.

But finding ways of ramming air into a rocket engine is looked at in a lot of novel ways. The pay off is pretty huge.

Once you are reusing your first stage it starts to make more sense, because you are not throwing jet engines away, and because they assist with tidy landings.

_________________
What goes up better doggone well stay up! - Morgan Gravitronics, Company Slogan.


Back to top
Profile ICQ YIM
Space Station Commander
Space Station Commander
User avatar
Joined: Wed Aug 18, 2004 8:47 am
Posts: 521
Location: Science Park, Cambridge, UK
Post Re: Jet engines as boosters   Posted on: Wed Feb 10, 2010 11:22 am
I had assumed (but not typed out) that the jets would be recoverable - either jettisoned from the stage and parachuted down, or the entire first stage being recovered. You could even have then mounted on a ring and discarded in one go (and with decent software, you could probably have a powered landing in the same vein as AA but with jet engines)

But I see the point about weight - the question I guess is whether the saving in lox by using jets to help initial ascent is offset by the mass of the jets and pipework.


Back to top
Profile
Space Walker
Space Walker
avatar
Joined: Mon Sep 21, 2009 10:43 pm
Posts: 146
Location: Webster, TX
Post Re: Jet engines as boosters   Posted on: Wed Feb 10, 2010 2:48 pm
If using the same fuel type forboth engines, yeah i can see tehre being a weight savings at least. all depends on teh configuration.

here's another concept
http://en.wikipedia.org/wiki/Air-augmented_rocket

I am of the firm opinion that combined cycle engines are the way things need to go, at least until someone can design a new engine type that has the power of a rocket with the efficiency of a piston engine (or turbine, whichever floats your boat)

Heck, the Pratt & Whitney J-58 used in the SR-71 was for all intents and purposes a combined cycle engine. ( http://en.wikipedia.org/wiki/J-58 )
Transitioning from a turbojet w/ afterburner at lower mach to a "fan augmented" ramjet at higher mach. interesting enough, the faster it went, the more efficient it was. ingeneous design, and too bad you dont see it anymore (to my knowledge)

if you were building an aircraft launched rocket, conceivabley, you could have a system that was powered initially by small turbofan engines, that transitioned to fan augmented ramjets (a la J-58). above a certain speed/altitude, the turbofan would be isolated and a small rocket engine kicking in at low throttle (air augmented rocket config)until there is not enough air to use as external oxidizer at which point the rocket completely takes over. (lol sorry an idea popped into my head and i had to get it out)

:idea: of course, it does make me wonder, if you modify/design a turbofan in such a way that the oxidizer intake could be augmented by an internal source (Lox tank for example)essentially turning it into a rocket in and of itself. the big question is wether it could be made to provide enough power to be suffiecient....lol the brain is too active to be up to any good :twisted:

thanks for taking the time to read the ramblings of a bored engineer, have fun and rip away at it :P , I get alot out of these kinds of threads.


Back to top
Profile
Space Walker
Space Walker
avatar
Joined: Sun Apr 17, 2005 8:14 pm
Posts: 115
Location: Las Vegas NV
Post Re: Jet engines as boosters   Posted on: Wed Feb 10, 2010 5:17 pm
I don't think jet engines for rocket launchers make any sense at all. The best of them have a thrust/weight of less than 20 rather than 80-120 for rocket engines. Then juts cannot work beyond about mach 3, about 1/10 of orbit launch requirement (or 1/100 the energy). So why not use the little extra propellant mass (mostly the LOX) and use rocket from the ground up? The propellant is a lot cheaper than the extra engine.

Same goes for air launch. Adding an airplane to the launcher also makes no sense unless the ability to fly to an orbital plane for rendezvous is worth it (not done yet).

Charles Pooley http://www.microlaunchers.com/


Back to top
Profile WWW
Space Walker
Space Walker
avatar
Joined: Mon Sep 21, 2009 10:43 pm
Posts: 146
Location: Webster, TX
Post Re: Jet engines as boosters   Posted on: Wed Feb 10, 2010 6:25 pm
ckpooley wrote:
Same goes for air launch. Adding an airplane to the launcher also makes no sense unless the ability to fly to an orbital plane for rendezvous is worth it (not done yet).


I'm not sure I follow what you are saying here. Then again, re-reading my post, I realize it was hardly written well, lol.

I agree that pure turbojet/turbofan engines are not operable much beyond mach 3. systems like the J-58 as employed in the SR-71 went beyond that with is, and the limiting factor was the materials in the J-58 core. its been 52 years since that engine was first run, and I've often wondered what speeds might be possible if the same configuration was reworked with a modern, more powerful turbofan. but anyways....

Ok, I want to make sure I have something right here...
The difficulty isn't really getting to orbital altitude, but getting to the velocity necessary to maintain that orbit?


Back to top
Profile
Moderator
Moderator
avatar
Joined: Mon Feb 09, 2004 4:01 am
Posts: 747
Location: New Zealand
Post Re: Jet engines as boosters   Posted on: Wed Feb 10, 2010 10:32 pm
Go look at this guy:

Chrysler Phase A Shuttle Study - SERV

Best implementation I have seen. The Actual studies are linked at the bottom on the Nasa Server.

_________________
What goes up better doggone well stay up! - Morgan Gravitronics, Company Slogan.


Back to top
Profile ICQ YIM
Space Station Commander
Space Station Commander
User avatar
Joined: Wed Aug 18, 2004 8:47 am
Posts: 521
Location: Science Park, Cambridge, UK
Post Re: Jet engines as boosters   Posted on: Thu Feb 11, 2010 8:40 am
MFL wrote:
Ok, I want to make sure I have something right here...
The difficulty isn't really getting to orbital altitude, but getting to the velocity necessary to maintain that orbit?


Correct. If you don't have velocity around the Earth, then you fall straight back down. Each altitude has a particular velocity at which you are 'falling' but the rate of falling matches the orbital path. That would be the orbital velocity at that altitude. At geostationary orbit (about 22k miles), the rotation velocity is exactly the same as the rotation speed of the earth, so you don't appear to move relative to a point on the surface.

See http://en.wikipedia.org/wiki/Geostationary_orbit

and

http://en.wikipedia.org/wiki/Orbital_velocity


Back to top
Profile
Space Station Commander
Space Station Commander
User avatar
Joined: Wed Aug 18, 2004 8:47 am
Posts: 521
Location: Science Park, Cambridge, UK
Post Re: Jet engines as boosters   Posted on: Thu Feb 11, 2010 8:41 am
idiom wrote:
Go look at this guy:

Chrysler Phase A Shuttle Study - SERV

Best implementation I have seen. The Actual studies are linked at the bottom on the Nasa Server.


That's interesting - why did they choose jet engines for the final descent? Were rocket engines at the time not controllable enough? Or the computer systems needed not fast enough?

That thing looks a bit like the Blue Origin craft....but bigger!


Back to top
Profile
Space Walker
Space Walker
avatar
Joined: Mon Sep 21, 2009 10:43 pm
Posts: 146
Location: Webster, TX
Post Re: Jet engines as boosters   Posted on: Thu Feb 11, 2010 12:23 pm
lol, i've heard of the SERV before, and I thought the same thing when i saw the Shephard the first time...
what really catches my eye about the SERV is how they use Aerospikes, making them a part of the structure rather than as a nozzle off the back end like the "traditional" use. I wouldn't doubt that they way they wanted to use them on SERV would have negated the weight cost of the aerospike nozzle.

Not sure why the use of the turbojets either.... why not just relight the 'spikes? mayebe the engine tech, nozzle surface wouldn't withstand that?
Yeah, my guess wwas just that Chrysler didn't have the engine tech at the time of design proposal, but i suspect that the final design would have gone without the jets.

think a similiar (albiet, smaller) spike ring could be done with a set of Armadillo engines? lol would be fun to try.


JamesHughes wrote:
Correct. ...relative to a point on the surface.


Here's a thought, (caffine's finally starting to kick in...lol) use of a combined cycle engine similiar to what i described above (wether vehicle airlaunched or takes off from ground, dont matter) to get to altitude, or near altitude, then use of small solid rocket motors to push up to orbital velocity. then re-use the C-Cycle engines during the re-entry. From what Ive gathered in teh past, a good portion of the fuel comsumption of, for example, shuttle, is getting the mass through the high drag portions of the atmosphere. just makes me wonder if you weren't worried about gaining the orbital speed till at or near orbiatl altitude, if you could cut down on the fuel needed to reach said altitude. I know its not quite that simple, lol it is rocket science afterall...

I don't know why I am stuck on this thought process....lol. probably for the same reasons I'm stuck on some of the other projects I've currently got cooking (two... well now three, but only one is currently in reach, if i got the grant money for it. there's always a catch huh... :P )


Back to top
Profile
Moderator
Moderator
avatar
Joined: Mon Feb 09, 2004 4:01 am
Posts: 747
Location: New Zealand
Post Re: Jet engines as boosters   Posted on: Thu Feb 11, 2010 8:33 pm
It easier to do a combined cycle engine, or an air augmented spike like the N-1, when you have high forward velocity.

When you are landing, you have no low and everything is a lot lighter. Also the engines were hydrogen, when you come back from your orbital stay there might not be a lot of that left. So you get a nice dense storable jet fuel for landing.

_________________
What goes up better doggone well stay up! - Morgan Gravitronics, Company Slogan.


Back to top
Profile ICQ YIM
Space Walker
Space Walker
avatar
Joined: Mon Sep 21, 2009 10:43 pm
Posts: 146
Location: Webster, TX
Post Re: Jet engines as boosters   Posted on: Thu Feb 11, 2010 9:19 pm
well there is the thing about combined cycle engines... they are designed to work across a wide speed regimine(sp?).

if you use a combined cycle to get the altitude you need, and a strap on SRB to get the orbital velocity once at altitude, there should be no need for H2 on board. only the jet fuel (JP-7 is the obvious choice), and aditional O2.
that fo course assumes you could get a small turbojet core with reheater to run while being supplied by an internal oxidizer source. while challenging, i don't see a reason why it wouldnt be possible.

on the return, you'd be doing a glide entry similiar to Shuttle, so the amount of fuel needed would be minimal, if even needed at all. You'd assume that you'd be packing a margin of fuel for the up trip, so you;d likely have that margin on the down flight if needed. O2 would be needed only for the up burn, as coming down, you could just pull from atmo again.

I guess the proper term for such an engine would be more 'Variable Cycle' rather than combined cycle, as it is all one engine rather than 2 or more combined


Back to top
Profile
Space Walker
Space Walker
User avatar
Joined: Wed Mar 07, 2007 3:30 am
Posts: 213
Location: USA
Post Re: Jet engines as boosters   Posted on: Fri Feb 12, 2010 7:16 pm
Even if the design did not use O2 from the atmosphere it would be advantageous to simply use the atmosphere as reaction mass. I wonder if it can be done with geometry only and no moving parts.


Back to top
Profile WWW
Space Station Member
Space Station Member
avatar
Joined: Sun Dec 30, 2007 6:16 pm
Posts: 328
Post Re: Jet engines as boosters   Posted on: Mon Feb 15, 2010 9:22 pm
Depends. How much power do you have available, and are you worried about radiation? You might be able to trade Isp for thrust in the lower atmosphere...

At the moment I'm tending towards a Ramjet 1st stage, reusable and capable of Mach 6, with an 'expenable' (in the sense that it can't reenter) upper stage, replaced by a reusable craft for manned flights. Upper stages made out of plastic and carbon fibre for bonus points, since it can be reacted with Lunar oxygen to make CO2 and water.


Back to top
Profile
Space Walker
Space Walker
avatar
Joined: Mon Sep 21, 2009 10:43 pm
Posts: 146
Location: Webster, TX
Post Re: Jet engines as boosters   Posted on: Tue Feb 16, 2010 12:27 pm
DanielW wrote:
Even if the design did not use O2 from the atmosphere it would be advantageous to simply use the atmosphere as reaction mass. I wonder if it can be done with geometry only and no moving parts.


That's the idea behind an air-augmented rocket, essentially sticking a small rocket engine inside a ramjet. The problem though is weight. though... If you had an extra set of fuel injectors inside the air tube, and accelerated the system tojust above Mach1, then the rocket core could be used as the 'flame holder' of the ramjet until there is not enough atmo or worthwhile thrust genereated by the ramjust; then throttle up the rocket core.

In the end there is more than one way to skin a cat.
http://en.wikipedia.org/wiki/Ramjet#Int ... ted_rocket
http://en.wikipedia.org/wiki/Air-augmented_rocket

Terraformer wrote:
At the moment I'm tending towards a Ramjet 1st stage, reusable and capable of Mach 6, with an 'expenable' (in the sense that it can't reenter) upper stage, replaced by a reusable craft for manned flights.


I don't see why the ramjet's would have to be expendable... but i guess if you were going to have expendable engines...lol ramjets would by and far be the cheapest.


Back to top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 24 posts ] 
 

Who is online 

Users browsing this forum: No registered users and 11 guests


cron
© 2014 The International Space Fellowship, developed by Gabitasoft Interactive. All Rights Reserved.  Privacy Policy | Terms of Use