STILL OPEN TO IDEAS - SSTO loses tons of delta velocity before it even gets to space

[SpaceToad]

Hey all.

I updated to 1.0, and I decided to make an SSTO. Attached are some images.

My primary question is, how am I losing so much Delta-V before I even get to orbit! I am left with around roughly 1400m/s at my disposal once I get to 70k to circularize, making it impossible to rendezvous with my LKO station!\

Any help is appreciated.

Edited May 15, 2015 by SpaceToad

[Randazzo]

The large numbers are due to air-breathing mode. Air is free and endless and air-breathing engines burn significantly less fuel than closed-cycle rockets. Once you switch to closed cycle, you have only what you're carrying internally.

edit: This means it's also counterproductive to carry tanks that are full of oxidizer. You'll burn liquid fuel and air until you switch over to closed cycle, so that extra oxidizer will be dead weight.

[ScottyDoesKnow]

To add to that, if you change from atmospheric to vacuum in kerbal engineer you'll see the difference.

[SpaceToad]

Thanks! Any ideas on how to make it more efficient?

Edited May 14, 2015 by SpaceToad
Spelling...

[KerikBalm]

"I am left with around roughly 1400m/s at my disposal once I get to 70k to circularize, making it impossible to rendezvous with my LKO station!"

Ummm... 1,400 m/s should be plenty to circularize.

What ascent profile are you using?

By the time I get my SSTOs to 70 km, I only need about 200 m/s to circularize...

[SpaceToad]

Whoops. I made a kinda dumb statement there. What I mean is once I circularize, I only have enough left to deorbit. My method of ascent is 45 degrees to 10k, 5-10 degrees until 800-1000m/s, changing AoA to stay in the light reentry effects, Rockets at 24000, Stop burn when apoapsis at 70k, burn prograde to circularize. With this method, that is the case. Is this not the right way to do it?

[panzer1b]

SSTOs are pretty much a tiny fraction of what they were before 1.0 (and 1.0.2's increased soupy drag even moreso) hit. Im not saying they are impossible or useless, but now they have very bad payload fractions and tend to be extremely complicated/heavy/part count.

Also, since every single engine except the nuke and ions got a considerable ISP nerf, you will just not get that much range from anything anymore. Its gotten to the point that my capital ships have exponentially more range them my best cheaty (as in ion engines+ion fuel clipped into service bays) SSTO to laythe and back. Yes it is still possible to do crazy stuff with SSTOs like before, but it takes some truly impressive engineering to do anything now.

I wish you luck with your SSTOs, as much as i loved them, ive pretty much given up making interplanetary SSTOs as the only way to get very good interplanetary level range out of them is to abuse the aero/clipping to such as extent that you can nolonger call them legit. That or make them very large, something my machine doesnt like (not to mention i liek compact designs, which have been more or less killed off now 100%).

[GoSlash27]

Whoops. I made a kinda dumb statement there. What I mean is once I circularize, I only have enough left to deorbit. My method of ascent is 45 degrees to 10k, 5-10 degrees until 800-1000m/s, changing AoA to stay in the light reentry effects, Rockets at 24000, Stop burn when apoapsis at 70k, burn prograde to circularize. With this method, that is the case. Is this not the right way to do it?

SpaceToad,

There are more efficient ascent profiles, but that's not the problem being pointed out.

1400 m/sec is a *huge* DV budget for LKO operations. That's darn near enough to get you to Duna. My SSTO designs are built for 400 m/sec DV after circularization in closed cycle. Inclination correction takes about 40 m/sec per degree. Deorbit retroburn is about 26 m/sec. That leaves 150 m/sec each way for intercept/ rendezvous/ docking with some reserve.

Is the problem that your DV reading is based on the remaining fuel in air breathing mode rather than LF&O in closed cycle?

Best,

-Slashy

- - - Updated - - -

SSTOs are pretty much a tiny fraction of what they were before 1.0 (and 1.0.2's increased soupy drag even moreso) hit. Im not saying they are impossible or useless, but now they have very bad payload fractions and tend to be extremely complicated/heavy/part count.

Also, since every single engine except the nuke and ions got a considerable ISP nerf, you will just not get that much range from anything anymore. Its gotten to the point that my capital ships have exponentially more range them my best cheaty (as in ion engines+ion fuel clipped into service bays) SSTO to laythe and back. Yes it is still possible to do crazy stuff with SSTOs like before, but it takes some truly impressive engineering to do anything now.

I wish you luck with your SSTOs, as much as i loved them, ive pretty much given up making interplanetary SSTOs as the only way to get very good interplanetary level range out of them is to abuse the aero/clipping to such as extent that you can nolonger call them legit. That or make them very large, something my machine doesnt like (not to mention i liek compact designs, which have been more or less killed off now 100%).

Panzer,

Pish-posh! SSTOs are still alive and kicking, cheap,low in part count, and able to match the best payload fraction numbers of staged vertical rockets. They now have 1/2 to 1/3 the payload ratio they used to have, which now makes them competitive with conventional rockets, and they are no longer interplanetary.

This little guy represents a 20% payload fraction.

This bigger guy is 26% payload.

Best,

-Slashy

Edited May 14, 2015 by GoSlash27

[SpaceToad]

SpaceToad,

There are more efficient ascent profiles, but that's not the problem being pointed out.

1400 m/sec is a *huge* DV budget for LKO operations. That's darn near enough to get you to Duna. My SSTO designs are built for 400 m/sec DV after circularization in closed cycle. Inclination correction takes about 40 m/sec per degree. Deorbit retroburn is about 26 m/sec. That leaves 150 m/sec each way for intercept/ rendezvous/ docking with some reserve.

Is the problem that your DV reading is based on the remaining fuel in air breathing mode rather than LF&O in closed cycle?

Best,

-Slashy

Well, after circulation I have 178 m/sec remaining to work with. I am curious if this is a case for MOAR FUEL or if its just a bad design.

Also while we are on the subject, how to do increase the amount of Delta-V I have to work with in space?

Edited May 14, 2015 by SpaceToad

[GoSlash27]

Well, after circulation I have 178 m/sec remaining to work with. I am curious if this is a case for MOAR FUEL or if its just a bad design.

178 m/sec really isn't bad. Your design is sound and you can probably make up the difference with improvements in your launch profile and/ or a little tweaking.

Figure you need 40 m/sec to fix a +/- 1* inclination error and 26 m/sec to deorbit. That leaves a hundred m/sec to play around with, plus a little reserve. 50 m/sec to set up an intercept and 50 to rendezvous.

What's the altitude of your LKO station?

Best,

-Slashy

[SpaceToad]

178 m/sec really isn't bad. Your design is sound and you can probably make up the difference with improvements in your launch profile and/ or a little tweaking.

Figure you need 40 m/sec to fix a +/- 1* inclination error and 26 m/sec to deorbit. That leaves a hundred m/sec to play around with, plus a little reserve. 50 m/sec to set up an intercept and 50 to rendezvous.

What's the altitude of your LKO station?

Best,

-Slashy

The altitude of the station is 73k. I still need to send up a mission to install a jr. docking port adapter so the SSTO can dock if I am able to improve the profile and other aspects.

[GoSlash27]

Oh, in that case you've already got way more than you need to pull off the job. You have enough DV to dock with a station at 130km as it is.

If you'd like to up the efficiency a bit, there's some technique changes we can make and probably some tweaks also. Do you have a pic of your spacecraft?

Dumb question...

Okay, right off the bat you don't really need that structural intake under the tail. The 2 XM-G50s are adequate.

Launch profile:

You're good up to Mach 1 at 12km. Once you've hit 460m/sec and begin to see compression effects, pitch up to 15-20 degrees to just barely hold a light fog.

At 19 km, point the nose prograde until it hits 5* pitch. Let the nose drift up on it's own with SAS and leave it in air breathing mode until it's done accelerating (usually around 11-12 km/sec). Then switch to closed cycle and pitch up to 20*. Hold this until you hit 30 km altitude and then engage prograde hold and switch to map view to circularize normally.

Best,

-Slashy

Edited May 14, 2015 by GoSlash27

[SpaceToad]

Oh, in that case you've already got way more than you need to pull off the job. You have enough DV to dock with a station at 130km as it is.

If you'd like to up the efficiency a bit, there's some technique changes we can make and probably some tweaks also. Do you have a pic of your spacecraft?

Dumb question...

Okay, right off the bat you don't really need that structural intake under the tail. The 2 XM-G50s are adequate.

Launch profile:

You're good up to Mach 1 at 12km. Once you've hit 460m/sec and begin to see compression effects, pitch up to 15-20 degrees to just barely hold a light fog.

At 19 km, point the nose prograde until it hits 5* pitch. Let the nose drift up on it's own with SAS and leave it in air breathing mode until it's done accelerating (usually around 11-12 km/sec). Then switch to closed cycle and pitch up to 20*. Hold this until you hit 30 km altitude and then engage prograde hold and switch to map view to circularize normally.

Best,

-Slashy

Just curious, how did you calculate that ascent profile? If you dont mind, I would like to learn to make proper profiles to accommodate my future SSTO's.

[GoSlash27]

Just curious, how did you calculate that ascent profile? If you dont mind, I would like to learn to make proper profiles to accommodate my future SSTO's.

SpaceToad,

Oh, the profile is just the result of experience gained after launching a lot of SSTOs.

The dip at 12km is to push you through Mach 1. IME a single RAPIER can push up to 18 tonnes of spaceplane into the hypersonic regime if it's designed cleanly, but probably won't get supersonic unless it's in level flight at 10-12km or even a shallow dive.

After that, you want to ride the edge of compression effects in order to keep the speed up without wasting a lot of fuel to drag losses.

The pause at 20 km is to wring all the speed out of the RAPIERS in airbreathing mode you can get. a hundred m/sec here is a hundred m/sec left for you in orbit, so you want to be stingy without going overboard and running into overheating issues or excessive drag losses.

Going prograde at 30km is to minimize gravity losses and cosine losses during the ascent. Drag is so minimal up there that you may as well be in vacuum, so you just leave the throttle nailed and establish apoapsis.

This profile should yield good results for all of your spaceplanes regardless of size so long as they're in the 15-18 tonne per engine range.

Best,

-Slashy

[SpaceToad]

SpaceToad,

Oh, the profile is just the result of experience gained after launching a lot of SSTOs.

The dip at 12km is to push you through Mach 1. IME a single RAPIER can push up to 18 tonnes of spaceplane into the hypersonic regime if it's designed cleanly, but probably won't get supersonic unless it's in level flight at 10-12km or even a shallow dive.

After that, you want to ride the edge of compression effects in order to keep the speed up without wasting a lot of fuel to drag losses.

The pause at 20 km is to wring all the speed out of the RAPIERS in airbreathing mode you can get. a hundred m/sec here is a hundred m/sec left for you in orbit, so you want to be stingy without going overboard and running into overheating issues or excessive drag losses.

Going prograde at 30km is to minimize gravity losses and cosine losses during the ascent. Drag is so minimal up there that you may as well be in vacuum, so you just leave the throttle nailed and establish apoapsis.

This profile should yield good results for all of your spaceplanes regardless of size so long as they're in the 15-18 tonne per engine range.

Best,

-Slashy

Slashy,

You are the man. Thanks so much for your support. I truly appreciate it. +Rep for sure!

[GoSlash27]

Slashy,

You are the man. Thanks so much for your support. I truly appreciate it. +Rep for sure!

SpaceToad,

Thanks, I appreciate it! I take it you were able to see some orbital DV gains?

As you build up your SSTO ninja skills, you can pass on what you learn with the rest of us. KSP is definitely a community-driven enterprise.

Best,

-Slashy

Edited May 15, 2015 by GoSlash27

[Capt. Hunt]

You could also install some monopropellant tanks and OMS for orbital ops, they're alot more efficient in orbit then the RAPIER in closed cycle mode. Plus your Ascent isn't going to drastically eat up your supply and it'll make docking easier.

[GoSlash27]

You could also install some monopropellant tanks and OMS for orbital ops, they're alot more efficient in orbit then the RAPIER in closed cycle mode. Plus your Ascent isn't going to drastically eat up your supply and it'll make docking easier.

They are? That's news to me...

*edit*

Noo... I definitely disagree. The best monopropellant engine has considerably worse Isp than the RAPIER and mono tanks have an inferior wet/ dry mass ratio to LF&O tanks. They're definitely going to be less efficient. If they were still massless (they're not) then they could be theoretically more efficient in lieu of the RAPIER, but since you have to have the RAPIER to get to orbit in the first place, you'd have to tack them on. They would merely add mass for the ability to get worse Isp.

I definitely don't recommend this.

Best,

-Slashy

Edited May 15, 2015 by GoSlash27

[SpaceToad]

SpaceToad,

Thanks, I appreciate it! I take it you were able to see some orbital DV gains?

As you build up your SSTO ninja skills, you can pass on what you learn with the rest of us. KSP is definitely a community-driven enterprise.

Best,

-Slashy

I gave your ascent profile a try, but I have one question.

What do you mean by circularize normally. Like wait until apoapsis and burn prograde?

[GoSlash27]

I gave your ascent profile a try, but I have one question.

What do you mean by circularize normally. Like wait until apoapsis and burn prograde?

SpaceToad,

Aye. I run it with a little more detailed procedure, but that's pretty much the gist of it. It really just means "circularize the same way you would do it with any other rocket".

I burn lightly as necessary to maintain 70 km apoapsis with a final correction at 30 seconds out, then burn prograde to maintain a time to apoapsis of 5 seconds until circularized.

"I gave it a try" seems to imply that it didn't work out for you. No dice?

Best,

-Slashy

Edited May 15, 2015 by GoSlash27

[KerikBalm]

SSTOs are pretty much a tiny fraction of what they were before 1.0 (and 1.0.2's increased soupy drag even moreso) hit. Im not saying they are impossible or useless, but now they have very bad payload fractions and tend to be extremely complicated/heavy/part count.

Pffff... yea... terrible payload fraction, this cargo was only 33% of the mass, and if leftover fuel included, it had a 37% payload fraction.

and this one was so terrible, it only got its payload of a Munar lander + monoprop supply + batteries and solar panels for the science lab + a small refuel; to the Mun (and returned for a runway landing)

and look at this one, it came back nearly empty, so terrible.... except that it delivered 3/4th of an orange tank's worth of fuel to the fueldepot+ science lab in orbit of the Mun

As for the main question: this isn't 1.02, do not concern yourself about keeping the reentry effects light.

You should be going at least 1,100 m/s surface velocity (even higher if you already switched display to orbital) on turbos, and over 1,200 on rapiers.

And you should be doing this in a 15-20 degree climb at 20 km.

Get going faster on turbos/rapiers, and you'll benefit more from the oberth effect when you light rockets, you should also end up with a higher climb rate, getting your of of the draggy lower atmosphere sooner.

Perhaps you have insufficient TWR.

A higher jet TWR can get you going faster on jets, and a higher rocket TWR can help overcome drag and lift you out of the atmosphere.

If thrust = drag... you'll never get anywhere. If thrust =5x drag, then drag doesn't rob you of so much dV, and you should be climbing so that the air density is decreasing fast enough that the drag doesn't decrease, despite your faster speeds.

but also, don't climb too steeply.

[SpaceToad]

SpaceToad,

Aye. I run it with a little more detailed procedure, but that's pretty much the gist of it. It really just means "circularize the same way you would do it with any other rocket".

I burn lightly as necessary to maintain 70 km apoapsis with a final correction at 30 seconds out, then burn prograde to maintain a time to apoapsis of 5 seconds until circularized.

"I gave it a try" seems to imply that it didn't work out for you. No dice?

Best,

-Slashy

No. Lots of dice. 79k for 250k. Your ascent profile is the bomb. I just need to figure out how to circularize properly.

[GoSlash27]

No. Lots of dice. 79k for 250k. Your ascent profile is the bomb. I just need to figure out how to circularize properly.

oh, outstanding! looks like you've got it wired. And of course you can trade off that excess performance for extra payload as you go forward.

Congrats,

-Slashy