I submitted this to What-If, but it doesn’t look like they were interested so I’m asking the Dopers. Suppose a Space Shuttle, instead of being launched into low orbit had instead been launched straight up? How high could it reach and would it be able to land safely?.
For the first question one could take the total delta-V of a standard launch and calculate a straight up trajectory, but there are a lot of variables here. For starters the shuttle would clear the atmosphere sooner and encounter less drag; it would also pass through the maximum dynamic pressure more quickly and so have to throttle down its engines less, with fuel being used more efficiently the faster its burned. Also to be taken into account would be the contribution of the shuttle’s Orbital Maneuvering System rockets. In a typical launch they provide the apogee boost to establish orbit, retro braking to return to Earth, and any orbital changes in-between. How much if any of that do you count? Was the shuttle capable of carrying a payload of extra fuel for the OMS? If not, we’ll presume the shuttle is launching with crew but no payload.
As for the second question, I strongly suspect the answer is “no”. Reentry from orbit typically involves skimming the upper atmosphere given the returning spacecraft more time to slow down. A straight up launch would mean a mostly* straight down reentry, which I presume would be unsurvivable due to G forces and heating.
***** I presume the earth’s rotation would give it some lateral ground track.
BUT- what if some EMS fuel was reserved and when the shuttle reached to top of it’s trajectory added as much lateral velocity as possible, raising its perigee (which previously was somewhere near the Earth’s core)? And could the shuttle have gone high enough to reach (if the orbital inclinations were timed right) the Earth-Moon L1 point, at which point the Moon’s gravity would substantially change the outcome?
This question isn’t difficult, though you probably want to solve it with a numerical integration model in matlab, the problem is that many of the numbers you are asking for are not easy to find. What’s the coefficient of drag for this “straight up” flight profile? How much does the orbiter mass without “just crew”? What’s the exact thrust vs time profile for the SRBs?
Are you planning on throttling down to reduce drag losses in the lower atmosphere or is it firewalled throttles all the way?
It would be much easier to answer your question if we just assumed a generic rocket shaped object with the same dV as the space shuttle taking off perpendicular to the surface on a non rotating planet.
IIRC, the space shuttle’s trajectory was pretty much straight up until it passed through the maximum pressure point. Your proposed straight up course and the actual shuttle trajectory don’t really start to diverge until the shuttle is mostly out of the atmosphere. I don’t think you’ll see much fuel savings there.
I don’t know exactly how high it would go, but NASA has said that even if you pack it full of fuel instead of cargo it still couldn’t reach the moon.
No idea on the landing, but if you saved just enough fuel that you could alter your return path into one that hits the atmosphere at enough of an angle that you can skim off velocity using atmospheric friction, I’m wondering if the extra velocity from your maximum height path would mean that you have so much velocity to shed that you overload the heat tiles as it converts that velocity into heat.
I did a quick simulation in Perl and I get MECO at 9.92 km/s and 552 km height. That’s, uh, pretty fast.
No atmospheric drag calculations. Usually this is a pretty small factor for big rockets, though; a couple hundred meters per second (I did handle gravity drag).
No throttling at all. Peak accelerations reached 20 gees! Yeah, that’s not survivable. But I’m not sure how much of a difference this actually makes. Need to cap acceleration in the sim, but this is tough to do in a “realistic” way (can’t easily throttle the solids, etc.).
This velocity is enough to reach an apogee of 41,372 km (over geostationary height). The OMS engines have about 300 m/s of delta V, and by my math (Vis-Viva equation) a burn to raise perigee by Earth radius+400 km only requires 211 m/s. So it seems to be enough.
I think there’s probably just enough margin in here that if the atmospheric drag and acceleration are taken into account, you could just barely make it work. You aren’t getting back down, though. And I hope your pilot is on a diet.
No, I’m presuming a standard Kennedy Space Center launch. I did mention that the Earth’s rotation would affect the ground track.
I forgot that the engines have to be throttled back to accommodate the reduced weight as fuel is burned. Let’s say an imposed limit of 4G.
Strange that an ordinary Shuttle flight profile can only reach low earth orbit, but if we do a “pop fly” first you can get a high elliptical orbit for much the same fuel.
OK, so L1 is out, at least with the standard fuel load. Does anyone know whether the shuttle could carry extra OMS fuel as it’s payload? Maybe NASA never did it but it sounds like the sort of thing the USAF “Blue Shuttle” might have done.
The ordinary limit is 3 gees. It’s just a bit tricky to plug in since we have to balance between the thrust of the boosters vs. the main engines.
Peak acceleration occurred at the end of the flight, when the main tank is almost empty. Adding a payload dropped it by quite a bit.
Well, no payload makes quite a difference! I added in the maximum 25,060 kg payload and the velocity drops to 8.95 km/s and a peak apogee of 16,046 km. That is not high enough for the OMS engines to raise our perigee out of the atmosphere: we need to be at 30,000 km to get the delta-V requirement under 300 m/s.
I don’t know about carrying extra fuel, but it certainly seems possible in principle. The engines are rated for fairly long durations.
D’oh! I had a bug where the SSMEs were way overpowered. The performance did seem suspiciously high.
The total delta V was about right, but due to the large acceleration, the gravity losses were abnormally low. And this is really what kills you with a straight-up launch. With a normal launch, you gain height for free basically because the ground drops off below you (curvature of the Earth). That doesn’t happen here; every second you’re off the ground you lose 9.8 m/s of velocity.
I also modeled the engine performance more accurately (both for the boosters and SSMEs). The boosters start at 28 MN thrust and drop from there and correctly take Isp into account (I used an average before).
After this fix, acceleration never reached 3 Gs before separation. And after separation it was easier to model the SSME throttling, so I did that.
Anyway, after all these fixes, velocity at MECO is down to 6.24 km/s, and apogee is 5741 km. Nowhere close to enough to make any kind of orbit. Gravity losses at MECO were a whopping 4.75 km/s!
The Apollo direct ascent would have still done a normal launch into Earth’s orbit, then an insertion into a trajectory to the moon. The direct ascent part just refers to the idea of landing the whole rocket on the moon and then sending it home, rather than a small part of it (the lunar module).