Blowing up (almost) on reentry

[MajorMushroom]

Basically my damn science jr keeps blowing up. My speed is about 2000-3000m/s, which is crazy fast. Clearly my heat shields can't cope. I guess I'll have to aerobrake. So, do I literally just make a small orbit, and try and dip myself in? At what altitude? Thank you.

[nascarlaser1]

It all depends on the size of your ship, what orbit you are coming from, ect. Without more info I am not sure how to help .

[Razor235]

What are you trying to do?  Are you trying to deploy the science bay to another area, or returning data to kerbin?  If the former, you might just have to wait until you have a service bay large enough to stick it in, or fly it with a plane.  If the latter, you EVA a kerbal to take the data, or you can use the experiment storage unit that is in the same tech tree node as the Science Junior to bring it home, just right click on it and select "gather experiments" and it will suck in all the data from any instrument on the ship.  From there you can decouple it and land it separately or clip it into the command pod and bring it together, though beware this can mess up the aerodynamics on reentry.

[Geschosskopf]

Orbital velocity in LKO is over 2000m/s so that's the speed you always hit the atmosphere with.  And you have to descend to about 15km before the air starts getting thick enough to slow you down very much.  So there's nothing odd at all about going that fast, or even maintaining that speed for a long time.  And a 1.25m heat shield is perfectly capable of protecting a 1.25m part like the Science Jr through all that, provided you're coming down correctly.  From LKO, aiming to reach the surface about 90-120^ of longitude around from where you do the deorbit burn usually gives the right trajectory to avoid overheating and also slow you down soon enough to open chutes before impact.  If you come down steeper, you'll likely die in one of several possible ways.  If you come down much shallower than that, you'll likely skip.

Another aspect of "coming down right" with a heat shield the same size as the stack above it is to make sure you're dead on the retrograde vector.  If you're coming down at an angle, the upper parts of the ship will be exposed to reentry because the occlusive diameter of a heatshield is only a tiny amount wider than the heatshield itself.  Thus, it's sometimes better to use a 1.8m or 2.5m heatshield on a 1.25m stack.  And if you have any radially attached things, they'll burn unless you have 1 big heatshield wide enough to cover them, or they have their own  separate heatshields.

Edited September 18, 2017 by Geschosskopf

[bewing]

I'm going to guess you have the SciJr directly behind the heatshield? There is a problem with doing that.

The "area of protection" behind a heatshield is a narrow cone, flaring outward. But the bottom lip of the SciJr is bigger than the base of the cone. Which means it is still directly exposed to the plasma stream, and full heating.

To get around it, you can shuffle parts in your stack, or you can add some lightweight part between the heatshield and the SciJr.

 

 

[agrasyuk]

18 hours ago, MajorMushroom said:

Basically my damn science jr keeps blowing up. My speed is about 2000-3000m/s, which is crazy fast. Clearly my heat shields can't cope. I guess I'll have to aerobrake. So, do I literally just make a small orbit, and try and dip myself in? At what altitude? Thank you.

with speed of 3000 it sounds like you getting back from one of the moons. it was already noted that you can send another craft to recover data (and with some pain the module).

but if you have the time I'm thinking it is possible to slow your craft down enough in upper layers of atmo before going all in. it will take more then few orbits though . I'm currently working to stabilize oddly shaped craft coming from minmus to LKO. craft is not rated for reentry, no heat shield on it at all and not enough fuel to circularize without aerobrake . in my case at Pe of 54Km things are heating violently, but not blowing up, I do rotate the craft to expose different areas. now after revolution 3 AP dropped way past mun (I'm in the realm of ~3 hour orbits), I anticipate many more but I have the time. 

Kerbal alarm clock helps tremendously to plan activity around the aerobraking sessions.

Edited September 19, 2017 by agrasyuk

[MajorMushroom]

18 hours ago, bewing said:

I'm going to guess you have the SciJr directly behind the heatshield? There is a problem with doing that.

The "area of protection" behind a heatshield is a narrow cone, flaring outward. But the bottom lip of the SciJr is bigger than the base of the cone. Which means it is still directly exposed to the plasma stream, and full heating.

To get around it, you can shuffle parts in your stack, or you can add some lightweight part between the heatshield and the SciJr.

 

 

Ah, i didn't know that, thanks for the help. That's a frustrating thing up ol' junior. Guess ill have to work around it.

[Vanamonde]

Make sure the door is closed on the materials bay. It is much more vulnerable to heat if that is open. 

[VincentThacker]

Re-enter more aggressively instead of less. This will allow less time for the heat to build up. Ideally, the periapsis should be at around 15 km or less. Bring some radiators to dissipate the heat, or use a bigger heat shield

Edited September 22, 2017 by 100055

[Vanamonde]

11 hours ago, 100055 said:

Re-enter more aggressively instead of less. This will allow less time for the heat to build up. Ideally, the periapsis should be at around 15 km or less. Bring some radiators to dissipate the heat, or use a bigger heat shield

Yes. As counter-intuitive as this is, it does work. At least sometimes. 

[MajorMushroom]

I've been using the 2.5 m heat shield which is one size up, and that's helped. No problems yet!

[ussoldier2002]

On Tuesday, September 19, 2017 at 8:05 PM, Vanamonde said:

Make sure the door is closed on the materials bay. It is much more vulnerable to heat if that is open. 

How do you close the doors on the science junior? Once I use it and store data I can't close it.

[Vanamonde]

56 minutes ago, ussoldier2002 said:

How do you close the doors on the science junior? Once I use it and store data I can't close it.

You should get the option when you r-click on it. 

[ussoldier2002]

13 hours ago, Vanamonde said:

You should get the option when you r-click on it. 

I never do though. I've tried everything lol. It's always bothered me to reenter with the doors open.

[Vanamonde]

1 hour ago, ussoldier2002 said:

I never do though. I've tried everything lol. It's always bothered me to reenter with the doors open.

Do you have a screenshot of what comes up when you r-click the materials bay? 

[ussoldier2002]

2 hours ago, Vanamonde said:

Do you have a screenshot of what comes up when you r-click the materials bay? 

I don't have one but if I remember correctly I can review the data and/or reset the experiment. No option to close the doors. Same thing with the goo canister. I just assumed that was how they worked. Never thought something was wrong just a personal peeve (if you will) since it's aesthetically un-pleasing. I have family in town so I won't be playing again until next week but I will get you a screen shot then if you would like.

[Vanamonde]

The goo cannister can not close again. The mat bay is the only science part that does. You don't see this? 

[Spricigo]

14 hours ago, Vanamonde said:

The goo canister cannot be close again.

Worth mentioning that a scientist in EVA can [restore experiment] , it reenable the experiment on the otherwise single-use ScienceJr/MysteryGoo and as a side effect close it.

More to the point of the actual issue of reentry heat. Some less orthodox solutions:

-have the ScienceJr inside a cargo bay or 2.5m service bay.

-collect the science,  either with a astronaut in EVA or with a science container and abandon ther ScienceJr.