[1.0.5+] How to descend from Orbit in SSTO (question, answers, discussion)

[gilflo]

A short HD film to answer the question

SSTO with no shield and no radiators, well strut to sustain high G load.

Burn on retrograde, cockpit facing Kerbin, to be at 1500-1600 M/S at 60 kms, then, with help of cockpit Vernors flip 90 to 120° to belly to adopt a hight AOA re entry angle and maintain as long as possible.

When it becomes impossible you can select prograde to regain control before passing to manual.

First time, perfect re-entry

Second time, when you cannot maintain anymore, let it spin, issue will be a dive at 10 kms, then smoothly regain level flight....

 

 

 

Edited January 19, 2016 by gilflo

[Kerbal101]

1 hour ago, gilflo said:

(snip)
SSTO with no shield and no radiators, well strut to sustain high G load.

Burn on retrograde, cockpit facing Kerbin, to be at 1500-1600 M/S at 60 kms, then, with help of cockpit Vernors flip 90 to 120° to belly to adopt a hight AOA re entry angle and maintain as long as possible.

When it becomes impossible you can select prograde to regain control before passing to manual.

First time, perfect re-entry

Second time, when you cannot maintain anymore, let it spin, issue will be a dive at 10 kms, then smoothly regain level flight....

(snip)

Hai! 0:06 says all. Also the aircraft is very large with large wing area, with A.I.R.B.R.E.A.K.s.
I have even created retroactive-burning engines, specifically to perform breaking, like this: http://imgur.com/BEEufrs
Thats 8 extra tonnes, which guarantee soft landing. Payload, saving on which, would drastically cut the total costs - especially in carrier mode - about 88 ton less total weight on rocket.
But can you descend from 200km without retrograde burning, without automation(Mechjeb) and without A.I.R.B.R.E.A.Ks? Why? Because... for rocket, the typical thread is 3 posts long. It goes like this: "Q: Help, I am exploding on re-entry! A: Do you have heatshield? Q:Solved!"
A challenge of finding the method with minimum cost is always a good challenge. Descending from 70km half-orbit? "Just go spinning" (no, it would really work).

Edited January 19, 2016 by Kerbal101

[gilflo]

I can make aerobraking descending from 200kms, say Peri around 60kms, a lot of orbit to get an Apo at 80, then burn retrograde as long as possible before Cobra re-entry, it will save fuel.

Maximum overheating is between 55 and 30 kms. I am not sure airbrakes are very efficient.

Why no automation? In real life nobody would rely on human without help of automation...... In real life it's just impossible for a human to pilot whatever rocket aircraft at more than Mach 1

without any computer and automation help for flight controls.........

 

[gilflo]

On 19 janvier 2016 at 0:33 AM, Kerbal101 said:

Hai! 0:06 says all. Also the aircraft is very large with large wing area, with A.I.R.B.R.E.A.K.s.
I have even created retroactive-burning engines, specifically to perform breaking, like this: http://imgur.com/BEEufrs
Thats 8 extra tonnes, which guarantee soft landing. Payload, saving on which, would drastically cut the total costs - especially in carrier mode - about 88 ton less total weight on rocket.
But can you descend from 200km without retrograde burning, without automation(Mechjeb) and without A.I.R.B.R.E.A.Ks? Why? Because... for rocket, the typical thread is 3 posts long. It goes like this: "Q: Help, I am exploding on re-entry! A: Do you have heatshield? Q:Solved!"
A challenge of finding the method with minimum cost is always a good challenge. Descending from 70km half-orbit? "Just go spinning" (no, it would really work).

On 19 janvier 2016 at 0:33 AM, Kerbal101 said:

 

Well

I made a try: burn retrograde at 200 kms to get a 55 kms Peri, then at Peri burn to get an Apo of 72 kms. Just 1% fuel.

At Peri, I could have made it without using fuel, just some more tour....It was to gain time

Then at 72 burn retrograde from 72 to 65kms, it takes 10% of my fuel. 

Then at 65kms Cobra sitted on top of navball 80 to 85° and maintaining with cockpit vernors and RCS thrusters on direction for small lateral deviations

No speed brakes, as you see on Pic. Piloting manually is very easy....

Surface sped at beginning of Cobra was 1700m/s

At 43 kms, same speed and less  than half gauge overheating (512°)

At 37kms, speed 1576, heat 549°

At 30 kms, just before leaving for prograde, speed 1236, Mach 3.95 and heat 560, maximum heat was 649

So I guess, will get some heat under mach 4 and 30km on prograde, but not so much

I guess also we could have try without retroburning fuel

I made a film and give it a try with no retroburning tomorrow...

Edited January 21, 2016 by gilflo

[gilflo]

Today new try: I hyper edit to Orbit 72 kms. I can establish this orbit from 200kms by burning retrograde to get a 55 Peri, then Making a lot of orbits until Apo 72 is establish, then burn on APo to get a circular orbit, better to aim at Spacecenter. Total Coast 1-2% fuel

Orbit 72 kms, burning on retrograde at around 70° from Kerbin Spacecenter, aim 30 kms ahead of runway. I used the Landing guide from mechjeb to follow burning.

Cost 3.5% of my total fuel.

Surface speed at 72kms is around 1900m/s and won't change when we begin the flip to Cobra position at 60 kms altitude. Heat around 450° at this time.

I maintain Cobra position with small Vernor inputs and correct lateral deviations using RCS Thruster on direction mode (not roll mode or you go upset)

We got a maximum heat of 870° during cobra descent to 28 kms where speed was established under M 4.0 and 1100m/s, no speed brakes, no radiators, no cooling devices....

Then I go on prograde to stabilize, use pilot assistant to slowly decelerate speed and VS, this is the most difficult phase if you try manually as you are piloting on a "pin".

As my game was lagging i warp by 3 times, then finish manually on runway using 0.5% fuel.

Total fuel coast is around 4 to 5% of total fuel and SSTO is very easy to maintain in Cobra position, provided you really sit on top of Navball.

I can say obverheat is not a factor

Vid in line in 1 hour.

 

 

Edited January 21, 2016 by gilflo

[Orbin]

On 18.1.2016 at 4:35 PM, WhiteKnuckle said:

I've found that putting the craft into an uncontrolled tumble will keep the heating on any one part bellow maximum. Looks stupid, but it works as a last resort. 

This. I managed to successfully descend quite a few spaceplanes and rockets by just letting them spin uncontrolled. I always managed to regain control in lower atmosphere.

Also I'm kinda baffled noone mentioned the ass-first approach: When I'm worried about reentry but have some fuel left, I just enter the atmosphere facing directly retrograde and burn once the heat reaches uncomfortable levels. Like above, truning prograde/regaining control isn't a big deal once the air gets thick enough.

Another important thing that was only mentioned once is the CoM/CoL relation. When wrong it's really difficult to reenter, when right you can almost reenter hands-off-keyboard...
 

Also, what's you experience with speeds? For me, the make-or-break point seems to be around 1800m/s surface speed. Above that I'm sweating, but I can't remember overheating anymore going slower than that...

[gilflo]

Here is my vid where you can see that the Cobra Re entry is the best to loose speed between 60 and 28 kms while avoiding overheating.

I would even say that overheating is not a factor.....as you can see on the heating gauge juste under the altitude

I did it with a MK2 SSTO and get the same results. It was just a little bit harder to maintain the cobra position. The big Mark IV cargo has got plenty of belly surface that helps for that.

The trick to maintain the Cobra is really to sit on top on Navball between 80 and 90° AOA and to keep your Tail on 90° heading very precisely if you're coming from an equatorial orbit.

It's very important to maintain the tail on heading and for that you must use the Direction mode with RCS Thrusters, not the roll mode. The higher you sit on the Navball, the easier it is....

Edited January 21, 2016 by gilflo

[suicidejunkie]

I think your problem might be not enough wing, and thus not enough braking power.

My SSTMinmus spaceplane does the following for reentry:

1) Final approach from 80km AP, set PE at 45km

2) Pitch to 80 degrees, hold as long as possible for thermally cheap braking force (only the cockpit gyro to help at this point) and then let it settle to just above prograde.

3) At 45 km, pitch up to 45 degrees and hold while speed rapidly drops to 1600m/s and heat becomes non-threatening well before the parts warm up (monoprop puff engines on the nose are available in action group 4 in case fuel balance is off)

4) Coast in to land.  Throttle up the whiplashes and cruise at 22km / mach 2.5, if KSC is far away, or continue to pitch up and drop speed if KSC is close.

 

Note: Airbrakes are used for surface landing, and aren't applicable to the deorbit braking.  Puff engines are also used to flip into launch position on minmus and to arrest the flip from tail to wheels during minmus landing.

[Kerbal101]

19 hours ago, gilflo said:

Here is my vid where you can see that the Cobra Re entry is the best to loose speed between 60 and 28 kms while avoiding overheating.

I would even say that overheating is not a factor.....as you can see on the heating gauge juste under the altitude

(snip)

The trick to maintain the Cobra is really to sit on top on Navball between 80 and 90° AOA and to keep your Tail on 90° heading very precisely if you're coming from an equatorial orbit.

It's very important to maintain the tail on heading and for that you must use the Direction mode with RCS Thrusters, not the roll mode. The higher you sit on the Navball, the easier it is....

Thank you for this - but overheating is a factor. Thank you for video!

You see - your plane has pretty large wing surface, planes with smaller wing surface will have it a lot harder. While it was possible to do "Cobra" with 80 degree in 55km-45km, it easily flipped below. With small SSTO this is outright impossible or unrewarding - parts heat up much faster than speed goes down and at 45km it already overheats or flips.

Your suggestion:

"I can establish this orbit from 200kms by burning retrograde to get a 55 Peri, then Making a lot of orbits until Apo 72 is establish, then burn on APo to get a circular orbit, better to aim at Spacecenter. Total Coast 1-2% fuel"

ie, air breaking passes in atmosphere, is pretty interesting. But you indirectly basically confirm that direct re-entry from 200km is not possible, but - in my approach it is.
From 200 km, aim at 12km periapsis and lock autopilot to prograde. At 12km, go into stabilize instead. All stock guidance.

 

PS:
Invision Board Forum - sucks for how it handles basic quoting and destroys formating. In bold.

Edited January 22, 2016 by Kerbal101

[Kerbal101]

21 hours ago, Orbin said:

This. I managed to successfully descend quite a few spaceplanes and rockets by just letting them spin uncontrolled. I always managed to regain control in lower atmosphere.

Also I'm kinda baffled noone mentioned the ass-first approach: When I'm worried about reentry but have some fuel left, I just enter the atmosphere facing directly retrograde and burn once the heat reaches uncomfortable levels. Like above, truning prograde/regaining control isn't a big deal once the air gets thick enough.

Another important thing that was only mentioned once is the CoM/CoL relation. When wrong it's really difficult to reenter, when right you can almost reenter hands-off-keyboard...
 

Also, what's you experience with speeds? For me, the make-or-break point seems to be around 1800m/s surface speed. Above that I'm sweating, but I can't remember overheating anymore going slower than that...

My typical speeds is 2200m/s, when blackbird approach works.

Trying retrograde burning while even early grilling is pretty risky. The air-breathing engines have pretty low Tmax. CoM/CoL is pretty hard to achieve for small passenger aircraft (so that additional cabins are also crewable/passable).

I want this available early:

Edited January 22, 2016 by Kerbal101

[SSgt Baloo]

I have had some success with using loads of airbrakes on smallish spaceplanes to help slow them once they're in the atmosphere, but YMMV.

[gilflo]

On 22 janvier 2016 at 10:55 AM, Kerbal101 said:

Thank you for this - but overheating is a factor. Thank you for video!

You see - your plane has pretty large wing surface, planes with smaller wing surface will have it a lot harder. While it was possible to do "Cobra" with 80 degree in 55km-45km, it easily flipped below. With small SSTO this is outright impossible or unrewarding - parts heat up much faster than speed goes down and at 45km it already overheats or flips.

Your suggestion:

"I can establish this orbit from 200kms by burning retrograde to get a 55 Peri, then Making a lot of orbits until Apo 72 is establish, then burn on APo to get a circular orbit, better to aim at Spacecenter. Total Coast 1-2% fuel"

ie, air breaking passes in atmosphere, is pretty interesting. But you indirectly basically confirm that direct re-entry from 200km is not possible, but - in my approach it is.
From 200 km, aim at 12km periapsis and lock autopilot to prograde. At 12km, go into stabilize instead. All stock guidance.

 

PS:
Invision Board Forum - sucks for how it handles basic quoting and destroys formating. In bold.

Well, l can do it. When i select a negative periapsis from 72 kms to aim 30 kms ahead of Space Center runway it's a steeper approach than aiming a 12 kms peri from 200 kms.

then as long as i can maintain Cobra from 60 to 28 kms, i don't see any reasons i can't do it from 200 kms.

Another thing is that if i can maintain Cobra, belly facing prograde direction, in case of overheating, i can turn 180 on top of navball to have my back facing prograde to allow belly to become colder...i can tun on 360 degrees to struggle with overheating, not easy but possible. You just need to have a well balanced ssto.

when i got time i'll try that.....

[Kerbal101]

8 hours ago, gilflo said:

Well, l can do it. When i select a negative periapsis from 72 kms to aim 30 kms ahead of Space Center runway it's a steeper approach than aiming a 12 kms peri from 200 kms.

then as long as i can maintain Cobra from 60 to 28 kms, i don't see any reasons i can't do it from 200 kms.

Another thing is that if i can maintain Cobra, belly facing prograde direction, in case of overheating, i can turn 180 on top of navball to have my back facing prograde to allow belly to become colder...i can tun on 360 degrees to struggle with overheating, not easy but possible. You just need to have a well balanced ssto.

when i got time i'll try that.....

Thanks for response! No worries with "time", no obligations.
"You need to have a well balanced SSTO" - this is probably exact of my problems.

Yesterday I watched Jool landing video without any heatshields and found out two things:

- SSTO should have Center of Lift - behind - Center of Mass when descending. This causes it to have "heavy nose", which then strongly prevents any "flipovers"
- the perfect landing trajectory is not steep, but shallow. But not too shallow - about 20-30 degree negative to surface. Go too steep - overheat due to compression, go too flat - overheat due to lack of cooling.

[Evanitis]

2 minutes ago, Kerbal101 said:

SSTO should have Center of Lift - behind - Center of Mass when descending.

Indeed... but that setup is also best on takeoff. Ideally, SSTO planes should be designed so that the CoM doesn't change much (or at all) between empty and fully fueled. Easier said than done. The mod 'RCS build aid' can help by showing the wet/dry CoM in the hangar.. though I just empty the tanks when in doubt.

[gilflo]

Yes, it's true and very important to balance your plane as best as possible. And the mod you must have is RCS build Aid, because you can balance your aircraft for engine thrust, with or without fuel, for translation with RCS so as to set RCS thrusters at the best place and even balance it for attitude.

Here is a pic of my SSTO with no freight. The yellow circle is the COM full of fuel, the Red circle is the COM with no fuel but still oxidizer and mono prop and I could get the dry COM without any combustible.

So when you build your aircraft you have to make a compromise between all those COM to get the best balance in all situations and the best is when you COM don't move with fuel consumption, which is very difficult to get...

The center of lift, blue circle is behind the yellow and red circle and you can play on position of wing, tail and canard and rotation(angle with horizon) of tail and canard to adjust it.

Nose heavy is better for stability because when you accelerate the aircraft has a tendency to nose up, so it will decelerate, and then nose down to accelerate...and so on, but it is less confortable for maneuverabilty.

That's why i set Cockpit Vernors for the Cobra position....

Edited January 24, 2016 by gilflo

[gilflo]

Hi guys

Here is my contribution to MK2 SSTO Cobra descent where you will see that overheat is not a factor.

Burn retrograde from 200 kms to set a 12 Kms Periapsis, then Warp to 70 kms and begins Cobra at 60 kms of altitude, speed 2200 m/s.

Finish Cobra at 28 kms, speed 1120 m/s, then nose down to prograde.

Vernors engines under cockpit are tweak scale to 1.5, there are 2 but it if like they were 3.

Cobra was not as easy as with my Mark IV Cargo, but i struggle to maintain it and use all my oxy for that.

As you can see, overheat is not a factor.....

If you can't do it manually, try with your SAS in Radial + position and RCS.

Cobra position is no more than Radial + on Navball

 

Edited January 24, 2016 by gilflo