I wonder does is possible to go into space with small gravity overload?

[Pawelk198604]

I wonder does is possible to go into space with small g-force ? 

Edited December 1, 2016 by Pawelk198604

[monstah]

You have to explain your question better. Do you mean a low TWR rocket? Anything with TWR higher than 1 can throw itself up, and from there it's just a matter of having a big enough rocket. The lower the TWR, the more fuel the rocket wastes just hovering, and the (exponentially) more you have to bring with you.

That said, "big enough" might be hopelessly beyond our engineering capabilities for very low TWR, and I suppose anything with TWR lower than 2 is going to have a very hard time getting to space.

[kerbiloid]

If you have a high-thrust and high-ISP nuke engine and don't bother with fuel economy, you can ascent with any TWR > 1, just slowly.
You gain very gentle acceleration and negligible heating (because you are moving up with the speed of pedestrian).
But you spend very much fuel.

[Nibb31]

You don't necessarily need a high acceleration. You just need to go from 0 to 24000km/h. It's just easier to do it as quick as possible, because the less time you spend fighting gravity and drag, the less energy you spend.

[PB666]

w2r = g. g decreases with altitude but not much. YOu can fly approximately 1000 m/s on a winged vehicle up to about 20,000 meters.
Winged vehicles can stay aloft with TWR of 0.1 or less.

Once you get to about 1000 m/s with is 1/8 th velocity needed for and assume you are at the equator traveling at 400 m/s you get about 1400 m/s in orbital vector. You then

(1.4/8)^2 = 0.036 so you could do TWR of 9.96 and maintain inertia from the climb and eventually you would be far enough away from earth to accelerate.

 

[wumpus]

One thing that seems to be forgotten is that the Karman line (what you need to cross to get into space) is defined the height such that the velocity needed for lift is equal to the velocity needed for orbit.  So any lift-based flight that gets into space achieves orbital velocity.

Space planes simply don't go into orbit on Earth.  They are Kerbin-only.

If you want to use a spaceplane to get into orbit, a good idea of minimum thrust would be the X-43 (mach 9.6 flight).  It was released at mach 9.6, managed to maintain that speed, then started to slow down.  https://hapb-www.larc.nasa.gov/Public/Documents/AIAA-2006-1-317.pdf 

Obviously, you would need an additional (rocket) stage, but getting anywhere near mach 9.6 on air means you barely need any rocket to get there (the second stage of Falcon 9 starts from about mach 6: you might get away with getting something Dragon-sized with something half the size of the falcon 9 first stage).  But while the X-43 program showed that atmospheric (and atmosphere-breathing) flight was possible at mach 9.6, it didn't begin to provide a roadmap on how to get there.  It certainly didn't show much about how to accelerate to scramjet speed (other than using a relatively huge rocket), nor to haul a first stage from such speeds to a significant fraction of orbital velocity.

If you want to use a spaceplane to get into space, you will still need a second stage.  And it would probably look remarkably like spaceship 1 or spaceship 2.

[Jonfliesgoats]

Along the lines of what Wumpus said:

The X-15 is often cited as demonstrator of the feasibility of air-launched spaceplanes getting to space.  The problem is that the X-15 could only achieve sub-orbital flight.  The energy required to actually orbit was way beyond what could be packed into the X-15.  A craft capable of launching to orbit from the X-15s profile would have been way too heavy/big for a B-52.  The X-43 went super-duper fast, as Wumpus said, but getting it up to speed was a problem.

So for an air launched spaceplane to make it to orbit we have to do better in one or more of the following:

1.)Get more energy density from fuels (more energetic fuel/oxidizer/etc.)

2.)Do a better job of extracting energy from fuel (more efficient/powerful engines)

3.)Get much higher/faster before releasing our spaceplane (Supersonic/hypersonic mothership)

4.)Get a much bigger launch platform to release a bigger, more capable spaceplane (Put together two 747s)

 

[winged]

23 hours ago, Jonfliesgoats said:

 A craft capable of launching to orbit from the X-15s profile would have been way too heavy/big for a B-52. 

An-225 would be more than enough - MAKS System.

Edited December 3, 2016 by winged

[Jonfliesgoats]

The AN-225 with MAKS is certainly a good suggestion.  

Bear with me while I play the role of a naysayer.  The Mriys was built to haul the Buran shuttle around on its back.  Still, Buran itself is incapable of achieving orbit, and the payload is carried on the plane's roof, which has some inherent difficulties.  Even an airplane the size of a 225 can only get about 250 tons of payload flying by the time you put a spash of TS-1 into it.

So, even with an AN-225, by the time you put something like s MAKS system onto it, you are only getting s couple tons of payload to orbit via a very complex system with numerous points for catastrophic failure.  

Math to follow:

 

 

[Jonfliesgoats]

for simplicity's sake, let's forget about drag and just look at kinetic energy.  A ten ton object at 8km/s needs in excess of 320 Gigajoules of energy.

An AN225 flies at about .85 Mach, so figure a release of 275 m/s.  That gives the orbiter an energy advantage of roughly 378 Megajoules.

Energetically, we save less than 0.2% via a subsonic air-launch.  If we get generous with drag and gravity savings we are still talk talking less than 2% energy savings.

What is much more appealing would be an X-37, X-20 or Spyral type of system, if you want a flying aircraft in space.  It is much easier to get those things the energy they need by putting them in top of a rocket.

Finally, MAKS and Spyral are very cool!  If you are In Russia sometime, you should go check the Spyral on display!  

Stratolaunch is trying to cobble together a truely gargantuan mothership.  They are actually trying to put together a couple 747s, and the project appears to be very complex from my uninformed position.  It will be similar in mass to the 225, but carry more and fly hiher albeit at a lower speed.  Here's the link:

http://aerospace.vulcan.com/#stratolaunch

As an aside: The Polish Air Force was one of the best performing and least appreciated air arms of WW2.  Also, thank the Poles for radar.  In America we joke about Polish engineering because we are uninformed.  You guys make great planes and aviators!

Edited December 3, 2016 by Jonfliesgoats

[Jonfliesgoats]

The Soviets knew about the energy problems with air launching spaceplanes and spaceplanes in general.  Check out their proposed super/hypersonic mothership:

http://www.buran.ru/htm/molniya3.htm

For further reading, check out the proposed, manned Soviet space fighter:

http://www.astronautix.com/u/uraganspaceinterceptor.html