Shuttle Landings Not going to happen

[dire]

I recently landed two Mk2 craft from high orbit; one hopped into a brief solar orbit, and the other one came back from Minmus. Both dropped directly into the atmosphere from their respective positions. The Minmus craft had a Large radiator on the bottom of its cockpit and nose area. The solar craft required 4 passes to burn off speed and a number of 'simulations' in order to get the de-orbit sequence just right without exploding. The Minmus craft required only 3 passes, was able to descend through the upper atmosphere going 300 m/s faster than the other without exploding, and splashed down on the first try, even though due to a design error it was missing a control fin.

My conclusion is that the large radiator contributed a huge amount to the Minmus craft's success. Totally worth the weight. It also acted as a ski when I flopped over on Minmus touch-down.

Edited July 17, 2016 by dire

[klesh]

2 hours ago, klesh said:

Lastly, and I don't know if its helpful or not, but I dig it, is that I put 2x small radiators on the top of the cockpit, placed just riht that they almost look like a hatch on the top.   Theyre translated down to the surface of the shuttle and oriented just right that they look the part.  I activate both upon re-entry and I like to think it keeps the cockpit part cool enough by venting the heat through it and out the top.  Maybe it doesnt, but I like to think it does.

 

Here is a better shot of what I'm talking about.  Turns out I use 3.  Remember, they're attached to the cockpit and simply translated back, so they're not removing heat from the mono tank like it looks.

Edited July 17, 2016 by klesh

[davidpsummers]

22 hours ago, ForScience6686 said:

You must pitch up more than that to get the best drag.  For space planes that's usually above 30°, depending on design.  At that low of pitch, you're hardly generating drag and only slightly improving lift.  Staying in the upper atmosphere has the problem of generating heat with very little air resistance.  So you need to get down to the thicker air to help slow you down faster, as well as allow the heat to radiate into the surrounding air.  I've had better luck with steeper entries myself, but I design for a light re entry weight and hold aoa at 90° for maximum drag.  I then adjust aoa as needed for glide to the runway.

When I pitch up it is for lift, not drag.  There seem to be two approaches.  One is max drag so you slow down before you heat up.  The other is to use your lift to keep from dropping deeper into the atmosphere than you can handle as far as heating goes.  The latter you come in shallow and catch lift at 40 km (ish, maybe high 30s?) to control your descent.  The OP tried this last one but had a problem with spinning out, which I don't get.  A couple of points that might help.

-I do use airbrakes as I come in.  You put them in back and they help with the spinning out, and slowing faster never hurts, no matter which approach.  I've done my approach without them, but it easier with them.  (Other than that, I don't know why your plane is spinning out so I can't help on that).

-Also, it is easer if you are pitched up 15-20 from the horizon before you hit the atmosphere.  It i have touble with the plane not wanting to pitch up no matter what, I move fuel from a front tank to a back tank.  Though maybe a few more control surfaces would be a better way to go.

[AeroGav]

4 hours ago, davidpsummers said:

When I pitch up it is for lift, not drag.  There seem to be two approaches.  One is max drag so you slow down before you heat up.  The other is to use your lift to keep from dropping deeper into the atmosphere than you can handle as far as heating goes.  The latter you come in shallow and catch lift at 40 km (ish, maybe high 30s?) to control your descent.  The OP tried this last one but had a problem with spinning out, which I don't get.  A couple of points that might help.

-I do use airbrakes as I come in.  You put them in back and they help with the spinning out, and slowing faster never hurts, no matter which approach.  I've done my approach without them, but it easier with them.  (Other than that, I don't know why your plane is spinning out so I can't help on that).

-Also, it is easer if you are pitched up 15-20 from the horizon before you hit the atmosphere.  It i have touble with the plane not wanting to pitch up no matter what, I move fuel from a front tank to a back tank.  Though maybe a few more control surfaces would be a better way to go.

I go for the "pitch for max lift not max drag" approach, that means an AoA of about 10-20 degrees and not much more.    The advantage of this is you stay up high longer and may skip off the atmosphere a few times,  so the peak rate of heating is lower.   If you are heatsploding due to skin temp reaching max, this is a good method. 

 

The downside compared with coming in steeper, is that core temp may become a problem in the cockpit.   I build a lot of stuff with mk1 cockpit parts and looking at the heat data in the debug menus, the problem is heat conduction from the nose, wings etc.  warming up the cockpit over a prolonged re-entry, especially as the coekpit got less heat tolerance than the other parts the craft is made of.   Radiators can help with this , but do add some drag.   I've also tried retractable radiators inside a service bay - each time the craft skips above 40km, open the service bay and deploy the radiator, which helps get rid of the heat that built up on the last dip into the soup.

[davidpsummers]

3 hours ago, AeroGav said:

I go for the "pitch for max lift not max drag" approach, that means an AoA of about 10-20 degrees and not much more.    The advantage of this is you stay up high longer and may skip off the atmosphere a few times,  so the peak rate of heating is lower.   If you are heatsploding due to skin temp reaching max, this is a good method. 

 

The downside compared with coming in steeper, is that core temp may become a problem in the cockpit.   I build a lot of stuff with mk1 cockpit parts and looking at the heat data in the debug menus, the problem is heat conduction from the nose, wings etc.  warming up the cockpit over a prolonged re-entry, especially as the coekpit got less heat tolerance than the other parts the craft is made of.   Radiators can help with this , but do add some drag.   I've also tried retractable radiators inside a service bay - each time the craft skips above 40km, open the service bay and deploy the radiator, which helps get rid of the heat that built up on the last dip into the soup.

Yeah, it always the cockpit and the Mk1 is one of the trickiest.  (I've had it overheat on ascent!  To low a cimb rate after I switched to rockets.)  I have a space plane of each of the three sizes and the Mk1 I bring in the most shallow.  I have to be trying to climb before I hit the atmosphere.  I haven't had to use a PE higher than 30 km yet...

But, in the end, if you drop down slow enough, anything will work.  

[Reactordrone]

The Dynawing is unstable if you use all of the fuel (the centre of gravity moves behind the centre of lift) so you might need some low speed flight testing of the shuttle section and a few aerodynamic tweaks. I did  a couple of test flights and had an unrecoverable flat spin on the first one (the crew compartments survived impact) and a very low altitude recovery the second time with a successful landing. Both re-entries went into severe spins in the mid atmosphere so I think the problem is largely the design rather than the piloting.

Edited July 18, 2016 by Reactordrone

[ajburges]

On 7/15/2016 at 0:50 PM, Alshain said:

You need a lower Pe.  I know that sounds counter-intuitive, but trust me it isn't.  It's a matter of cumulative heat.  If you set a high Pe and glide forever during re-entry, the heat builds slowly up to a point of destruction.  On the other hand if you set a lower Pe, you gain heat much faster, but not as long.  By the time it gets up to destructive levels, the aerodynamic forces slow you down so it cools off again.  Try a Pe of around 10-20km on re-entry from 70km orbit and keep that nose up until the re-entry heating abates, after that you can nose forward and fly it like a plane on a steep descent.

Can you please explain how this would work both in simulation and IRL?

If we frame the problem in terms of every: we have a chunk of kenetic energy we need to dispose of. We do that primarily by converting it to heat by compression and drag. Given the same starting energy, the longer approach should give more manageable temperatures (assuassuming net positive heat dissapation in the craft).

[Alshain]

3 hours ago, ajburges said:

Can you please explain how this would work both in simulation and IRL?

If we frame the problem in terms of every: we have a chunk of kenetic energy we need to dispose of. We do that primarily by converting it to heat by compression and drag. Given the same starting energy, the longer approach should give more manageable temperatures (assuassuming net positive heat dissapation in the craft).

That's part of the issue, there is very little heat dissipation in space or near space.  There is nothing to carry it away.  That's why we need those giant radiator panels on the ISS.  On Earth you have air, wind blows, even in low wind speeds it's moving at least a little, and in fact heat causes the air around it to move (hot air rises).  Wind doesn't blow in space, so there are no air molecules to dissipate the heat energy into.  Near space there is some, but it's so thin it's not effective. Heat radiation is a very slow process.  The sooner you get into air, the faster it dissipates.  It does generate heat faster, but if done right your craft can usually take it.

Edited July 19, 2016 by Alshain

[ajburges]

12 hours ago, Alshain said:

That's part of the issue, there is very little heat dissipation in space or near space.  There is nothing to carry it away.  That's why we need those giant radiator panels on the ISS.  On Earth you have air, wind blows, even in low wind speeds it's moving at least a little, and in fact heat causes the air around it to move (hot air rises).  Wind doesn't blow in space, so there are no air molecules to dissipate the heat energy into.  Near space there is some, but it's so thin it's not effective. Heat radiation is a very slow process.  The sooner you get into air, the faster it dissipates.  It does generate heat faster, but if done right your craft can usually take it.

Ah yes I see. The idea is to reach the slightly denser region before bleeding most of the speed so you increase your dissapation rate before you sink as much heat into your craft.

From my own experience I can postulate on an alternative. If your craft has high thermal mass, it can easily limit total temperature below 1200 on even a shallow approach. MK3 bodies work well for this because of the mass vs volume effect. The temp guages on batteries may almost touch red, but they will simply stay there (unless you panic).

Though I must confess, a Pe of ~43 km (from LKO) has always been kind to me. It also allows easier calculations for phase of deorbit burn.

[ForScience6686]

So I completed the first test of this scenario this morning before work.  Coming in with a very steep reentry.  Now it wasn't a shuttle but I survived with hardly a temp bar showing up in the gigantors.  Dropping from just above 75km to splash down in between ksc and booster peninsula.  Had control issues at 900 m/s but held course for a runway landing.  This design could not hold radial very well, but still did very well with heat.  Had to use jets to make the final leg, but I had plenty of fuel for that.  Tonight I'll run it through a shallow entry and post the pictures in hopes to show the in ability to radiate heat in the upper atmosphere, and why I choose steep for heat issues as well as targeting the landing strip.

[T-Bouw]

Keep us posted about your progress okay @kirkmyster?

I've only done a handfull of shuttle-landings myself a few years back, so I'd like to know what's up nowadays.

[foamyesque]

I realize everybody in this thread's giving conflicting advice, so I'll add to it; I like to set my periapsis for a return from LKO to be around 45km, then fly with an AoA of between 40 to 50 degrees. This gives you fairly high but manageable heat loading, a long glide path with large cross-range ability, and cuts down on aerodynamic stresses. In order to keep your AoA up you need to balance your CoM and CoL for reentry very closely together, or else the aero forces will shove your nose prograde (or make you flip if you go too far :v) and make you lawndart. Some RCS is useful, like the shuttle used, particularly for pitch control during the reentry and for transitioning out of the stall and into a glide.

EDIT:

Also, it makes landing at the KSC pretty simple. Exact characteristics depend on your approach and so on, but if you stick your PE right above KSC I've found minor management of my AoA will regularly put me back at the runway,

Edited July 19, 2016 by foamyesque