boacvc10
Topic Author
Posts: 490
Joined: Tue Jul 25, 2006 2:31 pm

reducing launch cost - rocket with jet powered first stage discussion

Wed Nov 28, 2018 4:21 am

Has there been a rocket with a first stage comprising an air breathing high thrust/weight ratio jet engine for a short duration flight (say 3-5 miles altitude and gravity turn)? I did some rocket equation calculations once based upon pure chemical rockets and from what I could see if I ran a series of stages - most of the fuel expenditure is in the lower altitudes and thrust levels are high (hence many rocket clusters in lower stages of operational systems) - essentially the challenge of getting off the ground. So, if an air breathing jet engine was used for supercruise supersonic flight to lift a 2nd+3rd stage I am wondering what the hypothetical efficiency could be (assuming parachute back down).

yes/no? if not, then why not?
Up, up and Away!
 
User avatar
cpd
Posts: 5648
Joined: Sat Jun 28, 2008 4:46 am

Re: reducing launch cost - rocket with jet powered first stage discussion

Wed Nov 28, 2018 6:25 am

What size of rocket are you proposing? Wouldn't most be too large to be powered by jet engines (how many would be needed), and how should they get off the ground? Should they go vertically as traditional rockets do, or should they run along a launch track on a sled and then gain lift somehow as a plane does and then climb? That doesn't seem practical either.

Could a Boeing 896 or a similar machine carry a rocket aloft, then drop it and let the thing launch?

I'm reminded of the Shorts/English Electric proposal for G.O.R. 339 having a lifting platform for the vertical takeoff P17D part of the 'system' (the P17A would fly off from that) and all the engines apparently needed for that idea. Same with the Rolls Royce Griffith supersonic airliner, also equally outlandish. The potential of some of the engines not running properly would leave both machines very vulnerable. A rocket would surely face those similar problems.
 
User avatar
AirlineCritic
Posts: 1486
Joined: Sat Mar 14, 2009 1:07 pm

Re: reducing launch cost - rocket with jet powered first stage discussion

Wed Nov 28, 2018 7:26 am

See for instance the Stratolaunch project: https://en.wikipedia.org/wiki/Stratolaunch_Systems

But yeah, one can carry rockets in airplanes to an altitude to ease the launch. But it also brings its own issues. Now you'll have to most likely takeoff like airplanes, as the jet engines won't be able to lift you vertically. You have to plan for emergencies, and have your carrier aircraft be able to return to land with the rocket if it could not be launched. And the resulting aircraft are going to be big for the size of large rockets.

There are of course other approaches as well. For instance, railguns launching rockets: https://www.universetoday.com/73536/nas ... the-stars/
 
RJMAZ
Posts: 1013
Joined: Sat Jul 09, 2016 2:54 am

Re: reducing launch cost - rocket with jet powered first stage discussion

Wed Nov 28, 2018 7:44 am

It is only a matter of time until scramjets make a single stage to orbit possible.

You will have a turbojet to take off like a plane and go supersonic. The engine then turns into a scramjet similar to how the SR-71 turns into a ramjet. The difference is this will go twice as fast and twice as high as the SR-71.

You are now three quarters of the way into space from an energy perspective. A rocket then ignites to accelerate the aircraft into space.

This spaceplane could then have an internal launch bay that could boost satelites into higher orbits.
 
boacvc10
Topic Author
Posts: 490
Joined: Tue Jul 25, 2006 2:31 pm

Re: reducing launch cost - rocket with jet powered first stage discussion

Wed Nov 28, 2018 4:14 pm

cpd wrote:
What size of rocket are you proposing? Wouldn't most be too large to be powered by jet engines (how many would be needed), and how should they get off the ground?


I was thinking idly that a small gantry/vertical launch platform could be utilized to hold the stack, and the inlets for the air breating engines would be upward facing air scoops, whereas the engine output could be gimballed/thrust vectored or steered with adjustable exhaust louvers for directional flight.The jet engine center-line would be coincident with the center line of the stack. Now, if you extended this concept of a detachable "1st air-breathing stage", upon detachment, the air-breathing stage could pop wings out and power glide back to base for recovery on a skid | I'm thinking of a cruise missile type flight without terminal impact.

But for the lift phase: Someone correct me: Pratt and Whitney F119 (F-22 Raptor engine) 1800 kg dry mass (91 kN thrust). So approximate vertical lifting ability in sustained flight: 91000/9.81 kg -1800 kg - 1800 kg (upper stage structure) - 2000 kg (fuel?) - 5000 kg (lower stage fins, structure, controls) = ~3,100 Kg payload. Anything less than ~3,100 the payload will be accelerated upwards.

I mean, with "smallsats" being classed ~1 Kg to ~100 Kg, a 3000 Kg payload margin is very good for an upper stage, which will have to contain the orbital rocket motor (~500-1000 Kg) + orbital fuel, and somehow I think such a total system cost should be reasonable (obviously, substituting civilian engines designed for this purpose, with jet fighter thrust/weight ratio specifications).

What am I missing? Of course acceleration would be gentle and slower than a true rocket - but hey you get to reuse the air breathing lift stage (multiple launch opportunities per day!), and at altitude you then get to fire your rocket motor and off you go.
Up, up and Away!
 
User avatar
flyingturtle
Posts: 5466
Joined: Mon Oct 31, 2011 1:39 pm

Re: reducing launch cost - rocket with jet powered first stage discussion

Wed Nov 28, 2018 10:25 pm

Someone will do that in Kerbal Space Program...
Keeping calm is terrorism against those who want to live in fear.
 
426Shadow
Posts: 80
Joined: Tue Sep 11, 2007 8:13 am

Re: reducing launch cost - rocket with jet powered first stage discussion

Thu Nov 29, 2018 1:51 am

Thrust lapse might play a big role in why it hasn't happened. Rockets only gain power to weight ratio while jet engines lose it with attitude and speed to certain degree's. If it was practical then we would have seen it already.
Do it on three, One.....THREEEEEEE! Just got the nuts hangin out.
 
parapente
Posts: 2879
Joined: Tue Mar 28, 2006 10:42 pm

Re: reducing launch cost - rocket with jet powered first stage discussion

Thu Nov 29, 2018 9:58 am

Re RJMAZ's post.You are of course referring I presume to the Sabre engine being designed by Reaction Engines Ltd.Its been under development for a long time ( it's a difficult engineering task),it did receive an additional £60m funding from the UK govt this year and is working closely with EADS.
However whether it can really be achieved ( reliably) is another matter entirely.No one has ever combined 3 engines in one.Perhaps one day they will finally build one that can be properly tested but I doubt it will be in my lifetime.All the while progress of another kind is happening with conventional rockets to bring the price of launches right down.
Whether it be Spacex with the Falcon9 Block5 - a multi reusable first stage (they are about to launch one for the third time soon) or cheap disposable rockets made from spun carbon and additive manufacturing ( Rocket Lab's electron).By the time it's ready it may be too late.
For longer space trips Spacex is trying another route that has never been attempted before.
Their BFR/BFS-it is only a two stage rocket ( not efficient to To hauling all that mass up into space).But what Spacex will attempt to do is send up a second 'tanker' rocket and refill the craft in space.Its the key to getting to Mars.Everything rides on this concept.But never been remotely tried.
The only alternative is to use a nuclear engine for the second stage that has a far higher energy density and thus does not require refuelling.
The Americans got very close to perfecting an engine in the 1970's ( was successfully ground tested) before cancellation due to budget cuts.The Russians had a similar programme.From what we read the Russians have returned to the concept.
Long term if you want to go to Mars ( and come back) this will be the only practical way.
IMHO the Americans are making a mistake ploughing all their money into the SLS when they could be developing a nuclear thermal engine from what they have already learnt to create a proper second stage engine.First and third stages ( the bits that land wherever) would have to remain conventional chemical engines for obvious reasons.
 
RJMAZ
Posts: 1013
Joined: Sat Jul 09, 2016 2:54 am

Re: reducing launch cost - rocket with jet powered first stage discussion

Fri Nov 30, 2018 12:00 am

boacvc10 wrote:
But for the lift phase: Someone correct me: Pratt and Whitney F119 (F-22 Raptor engine) 1800 kg dry mass (91 kN thrust). So approximate vertical lifting ability in sustained flight: 91000/9.81 kg -1800 kg - 1800 kg (upper stage structure) - 2000 kg (fuel?) - 5000 kg (lower stage fins, structure, controls) = ~3,100 Kg payload. Anything less than ~3,100 the payload will be accelerated upwards.

Wow your calculations are way off. Pretty crazy idea.
Jet engine thrust reduces significantly with altitude.

Even if you started with a thrust to weight ratio of 2:1 at launch by the time you reach 30,000ft the thrust to weight ratio will already be back below 1:1. The launch vehicle wouldn't even make it to 500km/h vertical airspeed before starting to slow down. I doubt it would even make it to 40,000ft before reaching zero vertical airspeed. You would need twice the thrust to weight ratio of the F119 to even come close.

You could dump a rocket out of the cargo door of a C-17 at 40,000ft and it would beat your suggestion.

Stratolaunch would easily be the best option.

You want a cheap and cool option? Buy a Russian Su-27 and put your mini rocket on the centre pylon between the engines. Hit Mach 2, do a zoom climb and you'll be much higher and faster than stratolaunch which would offset the much smaller rocket.

Who is online

Users browsing this forum: jupiter2, mxaxai and 9 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos