Flight Question Sub-Orbital flights

[fullarmor2]

I'm interested in learning how to do sub-orbital flights correctly, especially since I did some research regarding special aircraft like the Concord and about space planes, which all could do this. So, when going from point A to point B on the Earth, how do you determine how fast and how high to go? When do you execute the deceleration burn? I'm currently flying the XR5 and I tried my first sub orbital flight from Wideawake to KSC. I just guessed to an extent about how fast and high to do it, and I burned until my flight line in the ground track in Map MFD reached KSC. But, I burned up during the reentry. So, how would anyone here do it? I'll give two examples and you tell me how you would do these sub orbital flights. The first, a shorter one, say, KSC to Ascension. The second a long one, say, Ascension to CSSC (Carl Sagan air base in the South Pacific). Thats all, thanks folks!

 

[ADSWNJ]

Well - you could try this for some inspiration! [ame="http://orbithangar.com/searchid.php?ID=3669"]KSC to Ascension Island in 1000 seconds (17 minute[/ame]

The general advice for starters would be to launch and climb as if you were doing a normal orbital insertion, then cruise half way and do a reentry as usual (eg 40 degrees AoA and glide home).

My Glideslope 2.2 add on is able to support suborbital hops, if you want some instrumentation.

 

[Urwumpe]

Usually, you don't need a deceleration burn - you only need to remember: The angle, at which you leave the atmosphere, will be the angle at which you enter the atmosphere. If you leave with 10° upwards flight path angle (velocity indicator to horizon) in 100 km altitude, you will reenter with 10° downward flight path angle in 100 km.

So, for most winged vehicles, it is better to fly shallow (less than 5° FPA), even if this is not the best for maximum range. If you would follow an optimal ballistic trajectory (about 20-30° FPA in that altitude), you would reenter to steep and burn up.

 

[fullarmor2]

Well - you could try this for some inspiration! KSC to Ascension Island in 1000 seconds (17 minute

The general advice for starters would be to launch and climb as if you were doing a normal orbital insertion, then cruise half way and do a reentry as usual (eg 40 degrees AoA and glide home).

My Glideslope 2.2 add on is able to support suborbital hops, if you want some instrumentation.

This didn't work. I launched out of Ascension and ended up going too high and fast and burned up on the reentry. Thanks for Glideslope 2.2 though. Its awesome. I use after my reentry from oribit. Its funny, I can go to the ISS, the Moon, Mars, and probably anywhere else in the XR5, but right now I don't know how to fly from one base to the other on the Earth in a sub orbital flight! I mean correctly. I can wing it and burn an insane amount of fuel somehow I guess.

---------- Post added at 07:07 PM ---------- Previous post was at 06:51 PM ----------

"Usually, you don't need a deceleration burn - you only need to remember: The angle, at which you leave the atmosphere, will be the angle at which you enter the atmosphere. If you leave with 10° upwards flight path angle (velocity indicator to horizon) in 100 km altitude, you will reenter with 10° downward flight path angle in 100 km.

So, for most winged vehicles, it is better to fly shallow (less than 5° FPA), even if this is not the best for maximum range. If you would follow an optimal ballistic trajectory (about 20-30° FPA in that altitude), you would reenter to steep and burn up."
I tried this from Wideawake to KSC but it didn't work. I flew out of Ascension and pitched to seven degrees. But , as I did that my pro-grade target in the HUD kept wanting to drop way down, more so the higher I got. So I had to use Hover to keep it up. I cut the main engine at around 4.5 KM per second at the half way point (around 4000km from KSC), and proceeded to do a reentry(just coasting) like I do coming back from the ISS or someplace. It didn't work for some reason. My vertical decent speed got too high and I burned up. I think that 4.5 km per second was too slow so I dropped to quickly from my 165 km altitude. And if I would have went faster then I would over shoot the damn base! I give up. No, really. lol

---------- Post added at 07:18 PM ---------- Previous post was at 07:07 PM ----------

Well, after experimenting I have two ways that I think will work at flying from Wideawake to KSC sub orbital (faster and higher to some degree than standard atmospheric flight) First way. Do a series of short hopping flights all the way there. Like a roller coaster, lol. This way you never go too high or too fast. The second way. Do one HUGE looping flight path all the way to KSC. I'm talking perhaps hundreds of KM at Apo. Then, on the way down use retrograde thrust to control your decent speed for a safe reentry.
If anyone has another suggestion let me know. :tiphat:

 

[ADSWNJ]

Glad you like the Glideslope. If you configure the target (say KSC) when on the ground, you'll get a standard reentry glideslope into Kennedy. Have it on vertical situation screen, and see if you can climb onto the glideslope. What do I mean? The VSIT screen plots altitude and true airspeed versus range to base. As you climb and accelerate, both of the trace lines should climb up to the reference glideslope. Once you hit it, cut engines and glide it home.

Some pointers - ideally you want to stay in the atmosphere, so have say an 80km altitude cap. If you are exceeding this whilst too slow then level out and continue to accelerate. If you are under 80km and exceeding speed, then throttle back and keep a gentle climb.

If you get on the reference glideslope, and you keep the reentry data in the green on the DATA screen (i.e. good AoA, good TAS, good Alt), then you should not burn up. Assuming you are flying an XR-5 or XR-2, then bring up the temperature display (and learn the kbd shortcuts for the attitude autopilot), to keep an eye on it. If it's too hot, then you need to lower the AoA to reduce the air resistance, and if it's still too hot, then you must be coming in too fast.

Have a play and let us know. If you keep on hitting Ctrl-S to save the scenario, then you can cut & paste the scenario into a [ CODE ] [ /CODE ] block (without the spaces) and I or others can look at your situation for you to give specific advice.

 

[Tommy]

You don't need to be at 5 degrees pitch during the entire ascent - only when you get to the edge of space (around 80k). If you had to use hovers to maintain a climb it means you were too high for your velocity.

You mentioned that your velocity was only 4.5 km/s. At that speed, you won't get sufficient lift above 55 - 60 km altitude. Also, your Apogee, at 165 km, is far too high for that velocity. 4.5 km/s is sufficient for a shorter hop like Ascension-Canaveral, but your apogee for that flight should only be around 100 - 110 km. An apogee of 165k would only be suitable for a flight that went close to halfway around the globe, and your velocity would be over 7 km/s at MECO.

The "five degrees" is a MAXIMUM, not a minimum. For a hop as short as AIA-KSC you would want a slope of about 1 degree at 80k alt.

Suborbital hops on a planet with an atmosphere won't be ballistic trajectories - and wouldn't use increased velocity to increase range as much as you would use skip re-entries.