Sub-G thrust to orbit.

Is is possible to make it into earth orbit using a sub-G thrusting
rocket motor together with a hypersonic lifting body?

Assuming it is possible Newtonically, is it possible thermally, i.e.
would the vehicle burn up due to atmospheric friction before it reached
orbit?

-Bruce tttt

"Brucebo" wrote in message
oups.com...
Is is possible to make it into earth orbit using a sub-G thrusting
rocket motor together with a hypersonic lifting body?

Assuming it is possible Newtonically, is it possible thermally, i.e.
would the vehicle burn up due to atmospheric friction before it reached
orbit?

Doesn't matter, because the only thing that matters is that such an approach
would be very high cost.

Jeff
--
Remove icky phrase from email address to get a valid address.

Brucebo wrote:
Is is possible to make it into earth orbit using a sub-G thrusting
rocket motor together with a hypersonic lifting body?

Assuming it is possible Newtonically, is it possible thermally, i.e.
would the vehicle burn up due to atmospheric friction before it reached
orbit?

There is nothing in theory preventing it working.
In practice, it seems to offer few advantages over a simple rocket
accellerating at maybe 3G maximum (like shuttle), even if you liberally
sprinkle the design with magic 'perfect insulators' and such.
Once you try to design an actual flyable vehicle, it seems likely that
the first thing you'll be generating for the first few billion dollars will
be research that might be interesting some day.

Brucebo wrote:

Is is possible to make it into earth orbit using a sub-G
thrusting rocket motor together with a hypersonic lifting body?

Yes. There have been many schemes of this type proposed over the
years. Most have involved airbreathing engines but all rocket
proposals have been made as well. Recently JP Aerospace has proposed
an ion rocket engined airship to orbit scheme.

Assuming it is possible Newtonically, is it possible thermally,
i.e. would the vehicle burn up due to atmospheric friction
before it reached orbit?

Most proposals of this sort involve regenerative cooling schemes to
prevent airframe and/or engine failure but low dynamic pressure paths
(like the JP Aerospace proposal) have also been examined.

Jim Davis

On 28 Feb 2005 11:02:17 -0800
"Brucebo" wrote:

Is is possible to make it into earth orbit using a sub-G thrusting
rocket motor together with a hypersonic lifting body?

Airfoils (including lifting bodies) lose efficency once they hypersonic.
That, combined with the higher drag at hypersonic speeds will make it
impossible to continue acceleration with sub-G thrust.
--
Michael Smith
Network Applications
www.netapps.com.au | +61 (0) 416 062 898
Web Hosting | Internet Services

Ian Stirling wrote:

There is nothing in theory preventing it working.

Follow-on question that steers away from hypersonic aircraft...

Is it possible for an upper stage to get to low Earth orbit with less
than 1G of acceleration (without using aerodynamic lift)?

Say it's a second stage. The first stage has given a 2400m/s kick, some
of that going to gravity losses. Can the second stage, with 0.4 to
0.6Gs thrust, make it to orbit?

Mike Miller

Technically, any vehicle with a subsonic, sonic, and hypersonic L/D
ratio greater than one can achieve orbit this way. Thermal protection
is not really the problem - the problem is energy.

Since you are now putting most of your thrust into overcoming drag, not
gravity - all that heat energy has to be provided by your engines.
That means that you will need much more fuel to acheive orbit via lift
than if your engines provided all (or at least most) of the lift.
Saving 50% mass of the engine at the expense of doubling your fuel
seems to be a bad idea.

It is dependant on your hypersonic L/D ratio, but for all reasonable
values you should sit your rocket on it's tail, not its wings. (Though
you could argue for a subsonic-sonic winged stage, it's mainly the
hypersonic region where you want to use only the engines for lift.)

-David

wrote:

Ian Stirling wrote:

There is nothing in theory preventing it working.

Follow-on question that steers away from hypersonic aircraft...

Is it possible for an upper stage to get to low Earth orbit with less
than 1G of acceleration (without using aerodynamic lift)?

Less than 1G, of course.
If you're not at 0 altitude, or 0 tangential velocity, then the force
gravity exerts on you is under 1G.
So, in principle you only have to have a few mm/s or less more than this
accelleration to achieve orbit eventually.

Say it's a second stage. The first stage has given a 2400m/s kick, some
of that going to gravity losses. Can the second stage, with 0.4 to
0.6Gs thrust, make it to orbit?

2400m/s.
To a first approximation, if this is straight up, it'll go up for 240 seconds,
or about 300Km.

G will be about 10% lower, so that's not possible.

If it's at 45 degrees, that's about 1500m/s tangential velocity.
Normal orbital speed is some 8Km/s, so at 6.5Km/s, the accelleration is
some 8^2/6.5^2, or 1.5 times less, or about 0.65G.

If launching west from the equator, you pick up about another 500m/s, so
that's 8^2/6^2 = .55G.

So, maybe.
But you're going to eat a lot of fuel compared to even a stage that can kick
out 1G of accelleration.

In article . com,
wrote:
Is it possible for an upper stage to get to low Earth orbit with less
than 1G of acceleration (without using aerodynamic lift)?

There's nothing fundamentally impossible about it. Saturn V launches
averaged less than 1.5G during the S-II/S-IVB burns to orbit.

The only real impact of lower acceleration is that reaching orbit takes
longer, meaning that your first stage has to supply more of an upward kick
to keep the upper stages out of the atmosphere long enough. Centrifugal
lift goes as velocity squared, which means it doesn't become important
until you're near orbital velocity. Until then, with no aerodynamic lift,
little centrifugal lift, and little thrust lift (at low acceleration, even
pointing the engines quite sharply down won't help much), all that keeps
you out of the atmosphere is that initial upward momentum supplied by the
first stage. So there's got to be more of it, and the first stage is
probably going to take higher gravity losses supplying it.

So yes, it's possible, but you do pay a price. It's less efficient than
having more thrust.
--
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