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Why my vessel crash before reentry finishes?


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I wanted to earn some money before I start to do my mun flyby. So I accepted to launch 9 tourists to a suborbital trajectory & orbital trajectory. And it will give me over 250k in funds and over 100 in reputation. So I did my suborbital things. And now I need to do my orbital ones, which is the one which gives huge money. So my first one went smoothly and successfully landed after 17 minutes via parachutes. And I needed to do my second one. Now , everything went smooth, even reentry, but then the red things in the screen wouldn't go away and I couldn't open my drogue chutes. So it crashed in ~700m/s. I reverted that and did it again and again  and it had the same ending, I could not finish my contract. Please help. Thanks.

 

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17 hours ago, paul_c said:

The intercept with Mun isn't even higlighted and you only know its successful until you arrive near the Mun, and no idea of the return trajectory either.

Mun is home. If You play career again You can get there and back with closed eyes half drunk.

17 hours ago, paul_c said:

You'd need to know and  trust the underlying orbital mechanics/science, and also have flown the vehicle pretty much spot-on to 0deg inclination (which isn't displayed until you do an upgrade).

On way back inclination do not play any role - You gonna orbit Kerbin any way.

17 hours ago, paul_c said:

And I don't have any probe control either so needed to send Val (Jeb's dead.....), my only remaining pilot..... 

Of course You have to send Kerbal! It is game about brave Kerbals! KerbalsSpaceAdventure. I always send Jeb before any probe. Because on the beggining I have Kerbals and no probe :)

17 hours ago, paul_c said:

Obviously its worth delaying the chute deployment if it says "unsafe" and its still slowing down! If its not, then you would probably need 2 chutes (and deploy one later or manually), knowing one will do a bit of slowing then get torn off.

Take more chute and set one drouge to deploy without questioning safety (tweakable) - it will break but slow You down.

  

On 1/11/2021 at 6:48 AM, Anonymous49 said:

I couldn't open my drogue chutes. So it crashed in ~700m/s

Set one drouge to separate staging.

Go to advanced tweakable.

Set it to open immediatly (hard word, cant spell it).

It will open and break but will slow You down. Then use other drouges and other chutes.

Tweak them to maximal deplyoment 10.

 

Edited by vv3k70r
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23 minutes ago, vv3k70r said:

On way back inclination do not play any role - You gonna orbit Kerbin any way.

 

 

I know but the point is, on the way there, I would strongly advise to "fly up" at 0deg inclination - which is of course facilitated by KSC being on the equator - but you need to actively fly the craft to keep it Eastwards. Fortunately KSP has enough 'slop' that you can fly to a couple of degrees of 0deg inclination, burn at an ejection angle vaguely around 45deg Mun ahead, and look at the map to ensure the Ap touches the orbital path of the Mun and you'll have an encounter.

I might try to shoot for Minmus without the helper info later.

ETA also the point is, without much fuel you'd shoot for a free return trajectory to the Mun. I needed to make an adjustment once I'd left the SOI of Mun after the flyby, to get the Kerbin Pe to 37km. With 30 parts, you're going to be marginal on fuel because you physically can't build a big rocket.

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1 hour ago, paul_c said:

I know but the point is, on the way there, I would strongly advise to "fly up" at 0deg inclination - which is of course facilitated by KSC

Any inclination crossing KSC at point in time. Kerbin is rotating.

1 hour ago, paul_c said:

With 30 parts, you're going to be marginal on fuel because you physically can't build a big rocket.

But You can abuse gravity assist paying with time.

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On 1/11/2021 at 5:53 AM, Anonymous49 said:

I know that, I am just asking how to decelerate in over 700m/s WITH ONLY THE USELESS SMALL REACTION WHEEL

Reaction wheels are absolutely useless for dealing with aerodynamic forces at high speed-- the aero forces are so gigantic that they swamp whatever the reaction wheel tries to do.  The only way to solve your problem is aerodynamically.

You've built a highly streamlined, front-heavy javelin, which therefore has a really high ballistic coefficient.  It's the poster child for a craft that's going to faceplant at Mach 2.  You need to find an aerodynamic way to get it out of its nose-first, pointed-straight-:prograde: attitude during reentry.

One super easy way to do that would be to just add a couple of steerable fins onto the very back of the craft, such as the AV-R8 winglet.  With those, you'll be able to steer the craft to point the nose upward (i.e. above :prograde: ) as it falls, which will generate drag and also a lot of body lift.  This will allow the craft to slow down to speeds that the drogue chutes can function.

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53 minutes ago, Snark said:

  You need to find an aerodynamic way to get it out of its nose-first, pointed-straight-:prograde: attitude during reentry.

 

Or the blindingly obvious.......turn to retrograde just before entering the atmosphere (eg using the reaction wheel) and keep it retro during the hot part of re-entry. You'll be facing retro anyway during the burn.

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1 hour ago, Snark said:

over 700m/s WITH ONLY THE USELESS SMALL REACTION WHEEL

As per my understanding, it was just that OP wasn't aware he should turn his craft retrograde, and keep that, no?

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49 minutes ago, paul_c said:

Or the blindingly obvious.......turn to retrograde just before entering the atmosphere (eg using the reaction wheel) and keep it retro during the hot part of re-entry. You'll be facing retro anyway during the burn.

Depending on the craft, that can work... but not necessarily.  For this to solve the problem, it requires two things:

  • The craft can't be too aerodynamically unstable when pointing :retrograde:.  For example, an extremely nose-heavy craft is going to be extremely unstable in a tail-first orientation, and when aerodynamic forces get really big, tiny fluctuations (which you get even with SAS) can suddenly blow up and the craft can suddenly flip :prograde: .
  • The craft's ballistic coefficient can't be too high.  Yes, a butt-first orientation is likely draggier than a nose-first orientation... but the real question is not "is it draggier" but rather "is it draggy enough."  For a ship that's long, skinny, and dense enough, even entering :retrograde: and holding that attitude might not slow it down enough for drogue chutes to do their work in time.

I agree, simple :retrograde: entry is ideal if possible, and personally I design my ships that way the large majority of the time.  But occasionally, circumstances are such that I need to design a ship whose reentry vehicle is more of a javelin... and in such cases I find that "use steerable fins to get a nose-up attitude" is more dependable and reliable for me.  YMMV, of course, that's just my own experience.

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Its up to the OP now. I don't think I've ever had success with a vehicle shaped like that. 3 pax yes; 5 pax no.

If its a bit marginal you can delay the chute reopening until 0.07 or even 0.1 (on its scale with 1 being 100kPa or 1 atm on Kerbin) - if you fit a pressure instrument to the vehicle, you can display the pressure and at ~4 kPa it should go from "risky" to "safe" chute deployment if its shaped like the command module entering backwards. But for other less draggy shapes, sometimes there's too much speed so you can delay the chute deployment and do it lower in the atmosphere. Its a shame the units aren't the same but there you go.

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5 hours ago, paul_c said:

If I kill a crewmember, I need to hire another one at a not insignificant cost.

Indeed! Early in the game I hired some crewmembers, but discovered that as you rescue them from LKO, the Mun and Minmus you add crewmembers to your roster... for FREE!

AND you probably get a few Kerbucks in the process!

Doing "endless" rescue missions can give you a fairly sizeable roster in no time... while they don't show up as money, they are, in fact, money in the bank!

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4 hours ago, Wobbly Av8r said:

while they don't show up as money, they are, in fact, money in the bank!

The Fund reward for rescue mission are not bad either.

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