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KSC to Ascension

tblaxland

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My conclusion is that this can be done by a highly skilled pilot in 1300 seconds... Apparently I am not skilled enough yet.
...my guess is that nothing under 1500 seconds is possible. I just don't think the XR2 has the fuel and thermal limits for anything else. Of course, if someone can prove me wrong... :)
...I've finally done a decent run. 1231s...
:lol: A couple of quotes to highlight the fun I've been having following this thread. Nice flight, AG. :speakcool:
 

Arrowstar

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Well, after many many burned up XR2s littering the atlantic, I've finally done a decent run. 1231s from wheel-start to wheel-stop and 20m 17s from wheel-up as clocked by the MET timer. I'm sure that with tweaking and practice, a sub-20m journey is easily possible - it's a case of losing 31s.

A few notes on the configuration:

  • Most of the APU fuel was dumped before flight, as was LOX
  • No passengers in the XR2 (config file), no payloads.
  • Dumped about half SCRAM fuel before flight as it never got fully used anyway, dumped remaining SCRAM fuel as soon as the diffuser doors were closed
Cruising speed was about 11km/s and reentry-profile was steep. Juding when to begin reentry so that you drop out of the sky on ASC is important. I ended up in a 60degree descent down to the base and only became subsonic about 20s before landing. As you can see, pretty much all the tanks were empty at wheel-stop (I even had a bit of fuel left to fire the retro engines on the runway to stop!)
How in the Probe's name did you make it in 1231? I've yet to do it under 1500 seconds. Please, share, if only in PM... that's ridiculous. I thought I was fast!
 

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some nice thoughts there epsilon, duely noted. I plan to draw up some 'rules' and final addon plans, then offer them to the community for critique. But I'm gonna be quite busy over the next week or so, so not sure when the dev will come.

great flight btw, gonzo.
Might I also note (this was pointed out to me in PM) that the XR2's basic flight characteristics (ISP, etc) should NOT be user altered for the run? I was recommend adding this to the rules, as it'll really simplify problems later. That is to say, if you have to mod a scn or cfg file to change the XR2, don't. :)

Would this be reasonable, at least for the 'Pro' class?


-----Post Added-----


Just completed another run, new personal best, 1515 seconds. I still don't see how 1230 is even possible, but hey. :)
 

agentgonzo

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I'll try and get a playback done soon (never done one before)and share it. I did modify the config file, but only to remove the extra passengers (I was figuring that lowering the fuel and running without passengers/payload wouldn't be considered cheating as it doesn't affect the 'vessel' itself, just the payload). Other than that, there were no modifications to the config files. I see it as akin to driving a rally-car in a race without excess fuel, shopping or kids in the back of the car, but without 'special' fuel, aerodynamics etc.

Some more details of the flight:

  • Once I got to altitude and speed to light the SCRAM engines, I turned those on and did an ascent with both SCRAM and main engines on full throttle, using the AOA to keep the hull temperature in the yellow/red and not burning up. As soon as the diffuser temperature hit the red, the SCRAM doors were closed and excess SCRAM fuel dumped.
  • I then accelerated to ~11km/s and cruised (inverted) at about that speed, using the upper atmosphere keep the altitude constant.
  • The ascent and cruise were used to align the flight-path directly over ASC. At this point I did a cross-transfer of most of my RCS fuel to the main tanks.
  • Once I reached the breaking point, I raised my altitude to be able to turn retrograde and fired the main engines and burned all of the main fuel to decelerate.
  • By the end of the burn there was just enough time to flip the vessel over to perform a 'normal' reentry, except with a steep entry profile (~60° AOA). The XR2 was now so low on fuel and passengers that it can survive steeper reentries than normal without burning up, but it was still going into the red. I used Aerobrake MFD to align the reentry to drop straight onto ASC.
  • Once velocity dropped to about 1km/s, I turned off the AOA autopilot and headed straight at the end of the runway (about a 60° dive) and cross-transfered all remaining RCS fuel to the main engines. Thinking about it, I could have made a faster descent by firing the main engines again on this descent.
  • Sharp bank over the end of the runway, deploy speed brake and landing gear and open retro doors. As soon as I touched down on the runway, hit both speed brakes and applied retro thrust to stop.
That was a very hot flight. I burned up about 15 XR2s on ascent from KSC and about another 5-10 on descent into ASC before I got it right. Judging at what distance from ASC to perform your braking burn is important so that as soon as that's done you flip over and start aerobraking and don't waste any time at lower speeds.
 

Juanelm

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Completed the flight with 1989 seconds. I only dumped part of the fuel before flight, everything else was as the "Takeoff to ISS" scenario has it. I sustained wing damage and lost the elevons; had to land using RCS!

Agentgonzo that flight sounds just about perfect. It is a very good idea to use the atmosphere to keep altitude down while still being able to accelerate to much higher speeds. In my flight I kept gaining altitude and the reentry was very vertical, I had to use the remaining fuel with hover engines to slow down the descent. It would be nice if the XR-2's Attitude hold autopilod could hold the craft inverted.
 

wehaveaproblem

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Might I also note (this was pointed out to me in PM) that the XR2's basic flight characteristics (ISP, etc) should NOT be user altered for the run? I was recommend adding this to the rules, as it'll really simplify problems later. That is to say, if you have to mod a scn or cfg file to change the XR2, don't. :)
Would this be reasonable, at least for the 'Pro' class?
Very good points that I agree with. I think fuel management should be allowed, as should having only 2 crew. But I don't think the actually specs of the vessel should be altered.
I think the combination of these three things will offer enough scope for customization, yet keep all racers within the same envelope.
 

agentgonzo

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Just completed another run, new personal best, 1515 seconds. I still don't see how 1230 is even possible, but hey. :)
I've just done another run, beating 20 minutes this time. 1191s. Playback is on orbit-hangar if you want to take a look:
[ame="http://www.orbithangar.com/searchid.php?ID=3669"]KSC to Ascension Island in 20 minutes[/ame]

No modifications were done to the craft. The standard XR2 launch to ISS scenario was selected, payload, passengers, fuel and LOX dumped before launch.

I may be able to shave up to a minute off this time by braking later and lower and having a steeper descent onto ASC. I could probably raise the cruise speed to 11.75km/s or possibly 12km/s, but that will be really pushing it.
 
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MeDiCS

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YAY! Just did it!
After numerous disintegrated XR2s, I was finally able to land on WI. 34:53 minutes. Now I need to practice more...
 

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After watching that playback, I think I have a much better idea of how to do this flight. It seems like he got just about everything right, I didn't see much that could be improved. Nice work, agentgonzo! I'm going to see if I can't recreate your run tonight. :)
 

wehaveaproblem

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Great stuff Agentgonzo! you've really stirred things up now... and prematurely put yourself at the top of the as-yet-unreleased official league table. grats!
 

Epsilon

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I actually learned something important from AgentGonzo's playback - I didn't know you could get 1MN out of the SCRAMs. o.o

Now that I've seen it, I get how it works, but the knowledge is the important part. I also learned that the hull can heat a lot more than I've been heating it, which means I've been doing some weaksauce re-entries. *grin*

Funny thing is, just before seeing AG's playback, I did a run in 1513s - but I had a pair of aux fuel tanks to work wth as well. >_>

Incidentally, that's another thing to rule on... ^_^

Of course, you're trading off weight for fuel, and it makes it a bit touchy to get off the ground, but you're reentering a hell of a lot lighter than you took off too, and with more fuel for that deorbit burn.

:blahblah:
 

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Well, just did it in 1280, definitely a new best time for me. It's no 1231 seconds, but it's close!
 

Juanelm

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Agentgonzo I'm thinking how it would be possible to optimize even more that path you took. I'm thinking if it would be possible to accellerate to an even higher speed, using hover thrusters to mantain altitude (just as you recommend not to do ;) ), and use up all the propellant for acceleration, then perform all the braking with the atmosphere only. I've been trying it, and it's very, very hard, but maybe possible.
 

agentgonzo

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Hehe... this is getting silly. I've now done it in under 1100s! Some of the stuff that I'm trying to pull goes way beyond insanity. Under 1000s is my ultimate goal, but I doubt very much if this is possbile. I'd love to be proved wrong.
 
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Arrowstar

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What was your trick to getting your time under 1100 seconds? I mean there comes a point where you simply can't re-enter any faster or fly any faster above the atmosphere. :p
 

James.Denholm

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Just got around to watching the re-play, agentgonzo. I say this in the nicest way possible: You are nuts. That's the most insane flight I've ever seen!
 

dougkeenan

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Loved the little factoid tucked in the middle too. Here I am trying to follow everything that's going on then bam that pops up. :)
 
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