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Author Topic: Proper reentry procedure  (Read 3368 times)
Vinny003
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« on: November 25, 2015, 04:45:14 PM »

Hi, guys!

I don't know to re-enter the earth's atmosphere after a return trip from deep space say 1,000,000 or 1,500,000 kilometers away from earth? How do I tell if the command module is in the proper attitude for re-entry from deep space say 1,000,000 or 1,500,000 kilometers away from earth? Does the astronauts set the autopilot in the real command module for re-entry into the earth's atmosphere? And how do I get the autopilot to do the re-entry? Thanks!

                Cheers,
             Vincent
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Vinny003
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« Reply #1 on: December 27, 2015, 01:16:01 AM »

Hi, guys!

Is everybody here? Please tell me what is the proper reentry procedures? Thanks!

                 Cheers,
           Vincent
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pattersoncr
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« Reply #2 on: December 27, 2015, 10:31:00 AM »

You could, of course, follow the word file checklist included in your NASSP download.
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Vinny003
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« Reply #3 on: December 27, 2015, 04:59:08 PM »

Hi, pattersoncr!

Is there any updated reentry checklists. I think the reentry checklist in the NASSP download is old but I'm not sure. Thanks!

                    Cheers,
               Vincent
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MrFickles
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« Reply #4 on: January 10, 2016, 02:49:00 AM »

You'll need to know a few things,
1) GET at entry interface
2) Lat/Lon of splashdown point
3) How to enter data on the DSKY
4) How to do an IMU alignment.

To know whether you're in the proper orientation for reentry, run a P52 (option 2) realign, enter your GET at EI on F06 34, and complete a normal realignment. The FDAI will now show LVLH orientation at EI. As long as your pitch is around 180deg, you will reenter heatshield first.

Now, to set the autopilot to do the reentry, run P61, on F06 61, enter your splashdown lat/lon on R1 and R2, R3 must be -00001 unless your entry angle is too shallow (shallow enough to risk skipping out).
PRO until you see F50 25 with 00041 on R1, it's now time jettison the SM.
After jettisoning the SM, ensure SC CONT is in CMC and it's on AUTO.
Hit PRO again, autopilot will now maneuver to the reentry attitude
PRO again.
Autopilot is now set for reentry. Just sit back and relax.

Now this is just an extremely simplified procedure for setting up the autopilot and how to get you on the ground. There are a lot of useful information on P61 through P67 that's used to monitor the reentry, I'd be happy to explain in further detail if you're interested.
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Vinny003
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« Reply #5 on: January 13, 2016, 04:38:17 AM »

Hi, MrFickles!

I'm now using the VAGC Apollo 8. What is the proper reentry procedure for VAGC Apollo 8? I prefer not using the orbiter MFDs as they are very unrealistic. I prefer doing the procedure the realistic way, and I prefer strictly using the DSKY for SPS burns, maneuvers, reentry, attitude adjustment and stuff like that like what the real astronauts did!! Thanks!

                         Cheers,
                     Vincent
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dseagrav
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« Reply #6 on: January 14, 2016, 10:05:24 AM »

For Apollo 8, if you lost comm before TEI, you are stranded. If you lost comm before entry prep you are on your own. MCC computed those values and you have no means of doing it yourself. If you refuse to use MFDs you are stuck until MCC gets far enough to help you.
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MrFickles
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« Reply #7 on: January 15, 2016, 09:55:15 PM »

I agree with dseagrav, every space mission wasn't just about the astronauts, there was a large team of controllers on the ground as well. Think of the MFDs as mission control, having any information we need readily available through comms.

Now, for the procedure, typing out everything that you'll see when using the DSKY is too long and impractical, so you'll want to refer to this document: http://history.nasa.gov/alsj/a15/A15Delco.pdf
It's a AGC/LGC manual for Apollo 15, and it describes all programs that the CMC could run. Do take note that some of these programs weren't available on Apollo 8 due to a older 'software version'.
Everything you'll need though, is in that document.

What you'll need is:
P30 (external dV) and P40/P41 (SPS/RCS maneuver) for LOI, TEI and any midcourse corrections.
I'll assume you know how to use these 3 if you've gotten as far as reentry on Apollo 8.

P52 (IMU align) for realigning the FDAI to reference reentry attitude, you'll want to use option 2-Nominal for the align option, GET will be the time at entry interface.
P61 (reentry preparation) for the actual reentry, do take note that it advances automatically from P61 through to P67. Once you hit P63 though, there's nothing else to do on DSKY



P52 isn't critically important, unless pointing prograde or retrograde will put you roughly within 30 degrees of gimbal lock. Otherwise you can honestly just skip P52 and just use EMS for entry.

So, that just leaves P61 that you have to know how to use.
You'll want to run P61 with enough time to jettison the SM, reorient to the reentry attitude, and set up your EMS - 30mins before EI works.

As for the EMS,
Switch mode to 'EMS test' and scroll it to your inertial velocity at .05G.
Switch mode to 'RNG set' and set your range to splashdown.
Both of these can be gotten by hitting V16N63

Switch EMS mode to 'Entry' and activate EMS.
Finally, once you're in the proper orientation for entry,turn on 'EMS roll' and '.05G' on panel 1.


Now, you can sit back and relax, CMC is in control of the spacecraft. Of course, that's not what the astronauts would be doing during reentry, they would be monitoring the DSKY and EMS to ensure that the CMC wasn't going to burn the CM up, or skip out completely.

This is a EMS scroll you'll see

The numbers at the bottom represents velocity in kft/s.
From left to right, the lines curving down represents your maximum G buildup, you don't want your trace going down faster than the 'descending' line closest to your pointer or you risk burning up.
The lines curving up represents your minimum G to prevent skipout, you don't want your trace going up faster than the 'ascending' line closest to your pointer or you risk skipping out.
The vertical line at 25500kft/s represents orbital speed. Once past this speed, you cannot skip out.
The dashed lines with numbers represents the distance to go check lines, cross reference this with the numerical readout (which represents range in hundreds of NM) to determine over/undershoot at the landing site.
For example, if you're passing 4 on the scroll, but EMS reads 410.0, you're undershooting by 10NM. If it reads 390.0 you're overshooting by 10NM.

The pointer on the bottom left represents the CM lift vector. The lights on top and below of the pointer are the corridor verification indicators. Basically, when the light comes on (either top or bottom), the lift vector should be pointed towards the light.

In any case of:
Risk of burning up
Risk of skipping out
Lift vector pointed away from corridor verification light

Take manual control of the spacecraft (which is practically an aircraft at this point) and continue reentry manually. Using the distances check lines to aim the CM towards the landing spot.

EDIT: corrected EMS distance to go check. Thanks almostfm and indy91
« Last Edit: January 20, 2016, 11:07:27 PM by MrFickles » Logged
Vinny003
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« Reply #8 on: January 19, 2016, 03:57:00 PM »

Hi, Mr. Fickles!

Very informative! Thanks for the explanation!

                 Cheers,
              Vincent
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almostfm
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« Reply #9 on: January 19, 2016, 06:07:06 PM »


For example, if you're passing 4 on the scroll, but EMS reads 4100, you're undershooting by 100NM. If it reads 3900 you're undershooting by 100NM.

One of those (I'm guessing the one where the EMS says 3900) should mean you're overshooting by 100NMi.
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MrFickles
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« Reply #10 on: January 19, 2016, 11:31:54 PM »


For example, if you're passing 4 on the scroll, but EMS reads 4100, you're undershooting by 100NM. If it reads 3900 you're undershooting by 100NM.

One of those (I'm guessing the one where the EMS says 3900) should mean you're overshooting by 100NMi.

The numerical readout is your current range to go, and the dashed line on the scroll is the range you should be at. So if the numerical readout is higher than the scroll, it's an overshoot, and vice versa.
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indy91
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« Reply #11 on: January 20, 2016, 07:18:53 AM »

MrFickles, you wrote the word undershooting twice, I think that's all almostfm was pointing out  Happy

Also, the range potential lines are shown in 100 nautical miles, so 4 means 400NM. This thread reminds me that I should probably write down the EMS reentry procedures in the wiki, because the entry functionality is now fully implemented.
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MrFickles
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« Reply #12 on: January 20, 2016, 11:33:36 PM »

Wow, how could I not have noticed, thanks almostfm.

Just to prove how I did not proofread before posting, I meant 410.0 and 390.0 on the readout, thanks indy91 for pointing out that error
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