Shuttle Landings Not going to happen

[kirkmyster]

I have tried many times to get a shuttle safely on the ground, not back at the launch site just on the ground without success.  I either overheat and blow up or I get through the atmosphere then drop like a rock.  Please tell me there is a sure way to get a shuttle down, any shuttle back down without blowing up or falling like a rock.  Any ideas would be grateful. Thanks

 

~Kirkmyster

[bewing]

Yes, there are ways. It depends on the size of your "shuttle". Using that term gives me the impression that you want to build this out of MK3 parts?

In general, both those problems are the same problem. You do not have enough lift from the wings, and you do not have enough drag to slow down. The "not enough drag" problem can sometimes be solved by choosing your Pe on reentry very carefully, and by exactly how you fly the shuttle as it comes down. But then you are still left with the "not enough lift" problem. Which means that you need bigger wings and more of them -- which will add more drag, and will fix your other problem too.

 

[kirkmyster]

Yep, I am using the stock version of the MK3.  Trust me it was not easy to get that up in orbit with the orange tank.  So I deployed the tank and wanted to come back down.  I tried holding the angle at 20 or so degrees.  I am starting right at the edge too.  What is it?  70km or so.  Should I have the SAS on or off?  I tried off and always it goes into a spin which is not recoverable.  Think there is a "magic" angle you must use too.  Well like they say just press F9 and try again.

 

~Kirkmyster

[ForScience6686]

90 degrees to prograde until aero forces take over our you slow down enough to glide the rest.  20 degrees is still lower than than optimal lift angle around 30.  

[bewing]

As said above, pancake mode is what you want. 90 degrees the whole way until the ship can't hold it anymore. But you also didn't say what your Pe was set to. Try a 61km Pe.

[Alshain]

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.

Edited July 15, 2016 by Alshain

[kirkmyster]

@bewing

Forgive me still learning the space terms.  Pe?  My orbit is about 70km - 72km. Pancake mode another new term I have to learn. 90°? Is that one of the radial modes I think.  Hate being newbie at these things.  Guess I am thinking on how the real space shuttle does the re-entry with the nose in method.

 

~Kirkmyster

[Alshain]

10 minutes ago, kirkmyster said:

@bewing

Forgive me still learning the space terms.  Pe?  My orbit is about 70km - 72km. Pancake mode another new term I have to learn. 90°? Is that one of the radial modes I think.  Hate being newbie at these things.  Guess I am thinking on how the real space shuttle does the re-entry with the nose in method.

 

~Kirkmyster

Pe is Periapsis.  The lowest point in your orbit.   Not sure what pancake mode is, he is saying 90 degrees from prograde, so wherever prograde is, 90 degrees from that, that is using his method of very slow re-entry. (this is called "Angle of Attack" or AoA also abbreviated with the greek letter Alpha) I disagree with that however, if you use a lower Pe as I suggested, 30-ish degrees from prograde should be more than enough for a proper descent if you set a low Pe. (This is how the real space shuttle did it) The idea is to have your belly to the heat, which also means more drag because that also puts the flat edge of the wings toward the aerodynamic forces

I just looked it up, the shuttle AoA was 40 degrees.  I was close.

Edited July 15, 2016 by Alshain

[Daveroski]

When you build a shuttle, you are building a ship that goes up like a rocket but comes down like an aeroplane.

When you design this shuttle it is always a good idea to send it up on a sub orbital flight to test its flying-like-an-aeroplane abilities.

First just a short boost up to around 12000 and try to land the shuttle as though it had just come from space and was on final approach.

Then a sub orbital to 75000 to test it's fly-like-an-aeroplane ability in thinner air and at greater speed.

If you can land it after that... then go for orbit.

 

[bewing]

17 minutes ago, 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.

Sometimes a low Pe works. Most of the time it doesn't. A very high Pe always works. Pe's in the middle will kill you every time. And KSP's aerodynamics do not match real life. So matching the Space Shuttle's AoA will also get you killed.

There are two types of heat, skin heat and internal heat. Both can kill you. You build up skin heat by traveling at a low altitude very fast. You build up internal heat by traveling at a medium altitude very fast.

 

[Alshain]

Just now, bewing said:

Sometimes a low Pe works. Most of the time it doesn't. A very high Pe always works. Pe's in the middle will kill you every time. And KSP's aerodynamics do not match real life. So matching the Space Shuttle's AoA will also get you killed.

There are two types of heat, skin heat and internal heat. Both can kill you. You build up skin heat by traveling at a low altitude very fast. You build up internal heat by traveling at a medium altitude very fast.

 

I disagree again, it always works for me, and the aerodynamics simulation are not that far off from the real world. They certainly aren't 100% but they are close enough to make this descent work.  A very high Pe very rarely works, it's a good way to get you killed.

[bewing]

We should post some designs then, and have a little reentry competition.

[Alshain]

I found a video showing basically the same procedure I use.  This guy has guts though, his Re-Entry was incredibly steep even compared to mine.  I may have to try that, seems like it would be easier to target the runway, I just didn't think it would survive lol. (He does hit the runway a little hard, but you can fix that by flaring more)

https://youtu.be/T99shdw5XN0?t=2m25s

 

Edited July 15, 2016 by Alshain

[Daveroski]

As far as your pe goes, high, low, middling, it all depends on your ap.

The higher your ap the faster you will enter the atmosphere on your way to pe.

The faster your entry into the atmosphere - the more heat.

If you are returning from interplanetary then a high pe is best to slow you down and bring down your ap. Several obits of atmospheric braking may be needed.

To take advantage of the atmosphere lift your nose up to between 30 and 70 degrees. Somewhere in the middle should be best but again, it depends on the design of your craft.

If you are in a high orbit the same high pe may apply. I could thrown in an arbitrary height here but it really does depend on your design.

Best advice - if you have the fuel, reduce your both ap and pe to as close to atmosphere as possible and then reduce your pe to re-enter. This will make your re-entry speed lower and the atmosphere will be slightly less hostile.

 

 

[kirkmyster]

Wow!  Thank you everyone for this information.  I did not know it was this much too it.  Guess I have some more trial and errors to test out.  Thanks all again for this wealth of information.

 

~Kirkmyster

[ForScience6686]

I have also had good experience with the very low pe, but you need a light craft or very draggy craft.  Targeting the runway becomes much easier.  Your craft design plays a huge roll in what descent methods you can use.  One issue with a typical shuttle is the wings on the back.  That will pitch your nose down as you get into thinker air.  The design I try to use for space planes is to keep the wings in the middle of the craft.  Allowing greater aoa into the thicker air.  It all comes down to what you designed, and the struggles it will cause.

[TheDestroyer111]

14 hours ago, kirkmyster said:

and always it goes into a spin which is not recoverable.

This is a known issue on KSP replicas of the American space shuttle. It's nearly impossible to make a replica of it that doesn't get into an unrecoverable spin at some altitude during reentry. It doesn't matter if CoL is behind CoM, even if this is true with empty fuel tank, it gets into spins. The funny thing is that such spins rarely happen on low altitude atmospheric flights, they only seeem to happen after reentry.

The Russian Buran shuttle, however, is much easier to make in KSP and more aerodynamically stable. I failed so many times with attempts to make the American shuttle, I'm probably going to do all the STS missions with the Buran  

EDIT: Alshain below me, I said "nearly impossible".

Edited July 16, 2016 by TheDestroyer111

[Alshain]

1 hour ago, TheDestroyer111 said:

This is a known issue on KSP replicas of the American space shuttle. It's nearly impossible to make a replica of it that doesn't get into an unrecoverable spin at some altitude during reentry. It doesn't matter if CoL is behind CoM, even if this is true with empty fuel tank, it gets into spins. The funny thing is that such spins rarely happen on low altitude atmospheric flights, they only seeem to happen after reentry.

The Russian Buran shuttle, however, is much easier to make in KSP and more aerodynamically stable. I failed so many times with attempts to make the American shuttle, I'm probably going to do all the STS missions with the Buran  

It's not impossible at all.  If it's going into an unrecoverable spin, either the re-entry profile is wrong or the design needs work.  Many people have STS replicas.

[davidpsummers]

For the record, what I do is set a PE around 30.  As I come in, I am pointed maybe 20° above the horizon.  As I enter the atmosphere, I generate lift that slows my descent.  When I'm dropping maybe 50 m/s, I level off and continue the drop.   

Then it become a matter of dropping my altitude as a slow down.  As I loose speed my heating decreases.  As drop the in the atmosphere my heating increases.  And I balance those as the craft is too hot or has margin for error.  

Note, the rate of drop is not the amount of heating, but the rate of the increase in the amount of heating.  It takes time, that high up, to level off or climb, so you need to leave a margin of error.

These numbers will probably vary from craft to craft. So for a first craft I might set my PE to be 40 km, and point above the horizon until I have complete leveled off and then descent cautiously.

[dire]

I spent a silly amount of time yesterday getting a fairly simple Mk2 spaceplane splashed down on Kerbin. I tried to bring it in butt-first like a rocket but at 35km it would spin and the paper-thin cockpit would crush like a beer can, splattering poor Jeb all over his four passengers.

I finally managed to bring it in with a combination of three factors. First, I had my resident scientist collect all the data of interest in the cargo bay and store it in the passenger compartment with him, and I opened my cargo bay door and kept it open for the whole descent (It turned out the science project had similar heat tolerance to the cockpit, so it survived after all! But I thought it wouldn't). Next, I kept the aircraft high for a long time, spending fuel to keep it around 60km for an extra couple minutes. Next, I spent even more fuel (the final stage entered the atmosphere with an almost-full tank) to hit 35km going only 1500 m/s, which turned out to be just barely surviveable. Jeb could've had a BBQ with the floor of his cockpit!

The exact critical altitude and speed will vary from craft to craft; you may find that you discover several different altitudes at which you have a critical speed over which your craft explodes. I found that if I varied my AoA even slightly from dead prograde, the cockpit would explode, so I had to rely on anything else I could think of to make drag. Lower your landing gear if you've got it. Spend every drop of fuel retrograde between 55 and 35 km altitude -- it doesn't do you any good if you implode before you burn it.

Save early, hit alt-f5 to name your save files differently and save often! I highly recommend making a named quicksave just before you hit the atmosphere or jettison your next-to-last stage so that you can try many different approaches to the problem.

Edited July 16, 2016 by dire

[kirkmyster]

Conclusion - So I tried one more time to get down and land.  I tried bring the Pe to about 30km +/- 2km. That did help but this is what I am finding out.  I tried nose up 20 degrees.  No go. So I tried five to fifteen degrees works to about 30 to 40km and I think once you get there it is so fine that any pitch up or even down for that matter and you are going to spin and there is no recovery what so ever.  For the record this is the Dynawing if anyone would try and see what your results are.  I think it is a lost cause so be my guest and try.  Once again I thank everyone for the kind ideas and suggestions.  I might have to put flying shuttles on the back burner for a rainy or snowy day.

 

~Kirkmyster

[ForScience6686]

2 hours ago, kirkmyster said:

Conclusion - So I tried one more time to get down and land.  I tried bring the Pe to about 30km +/- 2km. That did help but this is what I am finding out.  I tried nose up 20 degrees.  No go. So I tried five to fifteen degrees works to about 30 to 40km and I think once you get there it is so fine that any pitch up or even down for that matter and you are going to spin and there is no recovery what so ever.  For the record this is the Dynawing if anyone would try and see what your results are.  I think it is a lost cause so be my guest and try.  Once again I thank everyone for the kind ideas and suggestions.  I might have to put flying shuttles on the back burner for a rainy or snowy day.

 

~Kirkmyster

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.

[dire]

My suggestion is maintain a low orbit over kerbin, and fly a 2.5m heat shield up with a klaw and stick it on the nose of your shuttle. I would bet that solves your problem.

Obviously, the margins are more generous with a 3.5m or 10m heat shield. But 2.5 should reduce the incoming heat to your cockpit and increase drag enough to solve your problem.

Edited July 16, 2016 by dire

[ForScience6686]

16 hours ago, dire said:

My suggestion is maintain a low orbit over kerbin, and fly a 2.5m heat shield up with a klaw and stick it on the nose of your shuttle. I would bet that solves your problem.

Obviously, the margins are more generous with a 3.5m or 10m heat shield. But 2.5 should reduce the incoming heat to your cockpit and increase drag enough to solve your problem.

That's not a needed fix for this.  His reentry profile is what needs work.  It was even stated that the shuttle used an aoa of 40° and he is using 20 and below.  Spins can be avoided by staying off the stick.  When traveling at such high speeds, control deflection is exaggerated and most often too much input is given.  I had the same issue with a space plane, I had to keep it set to radial until below 500 m/s before making course changes.  Otherwise flat spins would ensue.

[klesh]

I have an STS replica that works great.  One of the things I do is to use monopropellant tanks as ballast to help control my re-entries.  Its hard to see in this screenshot, but its the only one I have currently up on steam.  You will see Mk3 Mono tanks fore and aft of the cargo bay.  

http://steamcommunity.com/sharedfiles/filedetails/?id=681551622

I dont remember the numbers, but lets say each tank holds 1,000 units total.   At liftoff, i will have both tanks half empty(full?) at 500 units each.   This lets you put all 1,000 units onboard into either of the tanks depending on where you want your CoM.  I keep the Monopropellant in the cockpit as a reserve to replenish any I spend maneuvering in orbit.  

Another trick to help with orientation is to put a sufficient number of RCS jets about the nose.  I believe I have 2 on top, 2 on each side, and 3 under the nose, to aid in keeping pitch up lower in the atmosphere.  Make sure these are properly oriented 90°, and not simply surface attached pointing out and random angles.  

 

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.