Flight Question Help with deorbit, reentry and runway approach

[Mythos]

Hello everybody,

after many interplanetary trips with IMFD (learning TransX is still on my TODO-list) I want to improve my deorbit-, reentry- and landing-skills. For that I am learning to use Aerobrake MFD.

Here's what I've practised now some times:

• Start within XR5 in it's standard scenario "XR5/docked to ISS"
• Select Cape Canaveral in Map MFD and wait until my path goes over it second time (to reach target in daylight)
• Undock when near over Cape, path nearest a full orbit ahead
• Gain some distance to ISS and align Prograde/Retrograde
• Deorbit burn (Retro/Main) when ~ 3/4 orbit away, PeA to ~70k
• Wait for alt < 200k, set up Aerobrake MDF
• Use XR5's attitude AP to set AoA ~30° so Aerobrake MFD says I'll hit the target
• Set bank so Aerobrake MFD looks good for left/right (AP allows only steps of 5°)
• Go down watching the MFD and correct AoA (most times I have to reduce it slowly)
• The path down goes in waves, so I bounce upward some times but then come down again - This is not first class style (why?) but it works
• The heat reaches a max about 800 to 1000 - The ship can handle much more and I dont't get visible effects
• Try to have my base marker at 150 by banking to be nearly aligned with runway 15
• Set up COM/NAV to frequency of runway 15 but that comes in range too late for me to align better
• Come to slower speed very near to runway but very high
• Go down and land behind or beneath runway - most times soft, sometimes "injured" but not "destroyed"

So here are my questions:

• Is it a realistic reentry when I do so slow but with low heat?
• So would it be posible to do such slow that a heat shield would not be necessary / maybe reenter a damged vessel or with some doors open?
• Is there any help / MFD to tell me when to do deorbit burn while I'll still outside atmosphere of course? Without atmosphere I use 1/2 orbit, for earth I use some more (3/4) but don't set PeA to zero.
• How to calculate the deorbit burn so the path down looks good with always negative vertical speed?
• Is there some MFD to show my glidescope path for runway approach even before coming to signal range?

Maybe you can help me with that or point me to some tutorials I haven't found so far

 

[dgatsoulis]

Some orbinauts here, like to use the reentryMFD and GlidescopeMFD for their reentries.
I haven't used any MFD other than Aerobrake for my reentries. That and the stock SurfaceMFD to watch my vertical speed and more importantly vertical acceleration. Here are a few pointers:

Deorbit burn (Retro/Main) when ~ 3/4 orbit away, PeA to ~70k

It would be better if you tried a more aggressive reentry. Wait untill you are half an orbit away and aim for a ~66-67 km PeA

Wait for alt < 200k, set up Aerobrake MDF

You can set it up before reaching 200km, but you'll start getting meaningful data below that alt.

Use XR5's attitude AP to set AoA ~30° so Aerobrake MFD says I'll hit the target

The more aggressive reentry profile will allow you to have a higher angle of attack. Go for ~40°-43° - Don't go over 45° because you will sink in the atmosphere too fast and overheat as a result.

The path down goes in waves, so I bounce upward some times but then come down again - This is not first class style (why?) but it works
*The heat reaches a max about 800 to 1000 - The ship can handle much more and I dont't get visible effects

That's because of the low AOA you were using.

So here are my questions:
*Is it a realistic reentry when I do so slow but with low heat?

What you were doing is called a skip-reentry, which is a valid technic to use. If you are not satisfied with the results, try a more aggressive reentry.

So would it be posible to do such slow that a heat shield would not be necessary / maybe reenter a damged vessel or with some doors open?

Yes, it is possible. I haven't tried it with the XR5, but I've landed a DGIV once, without the canopy.

Is there any help / MFD to tell me when to do deorbit burn while I'll still outside atmosphere of course? Without atmosphere I use 1/2 orbit, for earth I use some more (3/4) but don't set PeA to zero.
[*]How to calculate the deorbit burn so the path down looks good with always negative vertical speed?

Perhaps reentryMFD, but I wouldn't know for sure, because I don't use it.
If you use the half an orbit rule of thumb, you should be fine.


Here is how I do it:

*Make the deorbit burn 1/2 orbit away from base. PeA ~ 67 km
*Set up AerobrakeMFD and wait for Alt to drop below 200 km
*Orient the spacecraft to an AoA of ~40°-43°
*Watch my predicted groundtrack on AerobrakeMFD. Apply a liitle bit of retro or main thrust if nessecary, to get the groundtrack to(very) slightly overshoot the base.
* Button-down the ship at Alt ~90 km
* Turn off the RCS thrusters and use atm control and CoG shift to maintain AoA, while watching the groundtrack on AerobrakeMFD. Bank if nessecary.
*Watch the VS and VAcc on Surface MFD, If the spececraft is getting hot, lower the AoA to gain some altitude.

After a few practise runs, you'll be able to land spot on anywhere you want.

Hope this helps.

 

[PhantomCruiser]

I've often reenter with an XR-5 and my temperature never get past the mid-point of the yellow indication (no re-entry flames either). At first I thought maybe I was doing something wrong, but apparantly I was doing it very well. As far as recovery with a door open? I'd avoid it at all possible, unless there was damage and couldn't be avoided.

You are already using aerobrake, but has you taken a look at BasesyncMFD? These two work together pretty well.

Also, take a look at GlideslopeMFD, it has a burntime calculator, and has a glideslope that you can follow that will take you all the way through re-entry, through the HAC and onto the runway. I've had intermittant success with it, but there are several Orbinauts here who love it (I just need to practice more with it).

 

[Cras]

I use a combo of DVTools, Aerobrake, Basesync, Glideslope, and IMFD to wonderful results.

 

[TMac3000]

dgatsoulis's signature: :rofl:

 

[Mythos]

Thank you all for your input :thumbup:

I couldn't find a reentryMFD in hangar but I tried Glideslope. BaseSync and Aerobrake I've got already. So I did my usual undocking and then set up all MFDs.

BaseSync told me closest passage is that I used before and I waited until one orbit to go. Then BaseSync deorbit program wanted some setup and told me ReA 2°, Ant 2°, RAl 80km would be usual. But with that it pointed deorbit to 1/4 orbit before target, that cunfused my 1/2 orbit thumb rule I learned. So I played with the parameters, reduced reentry angle (the one I can't explain but have the most idea of what it is) so I get a 1/2 orbit graph - Here I hoped the display would tell me 1/2 orbit would be best and not tune sth so the 1/2 orbit dogma comes out. To understand this and then be able to globalize the procedure to other planets the question now is, what is a good reentry angle and why that and not others? :hmm:

Then I tried Glideslope. After a while I got an idea of where to read the best time (distance) for deorbit burn but can't compare it to BaseSync (cant't find any readout, just graphical). Suddenly Glideslope went mad, took control and my XR5 started spinning around and I couldn't catch it. Glideslope also put out weird data and hyroglyphes for the base name. Change target ended in CTD :thumbsdown:
I'll give it a next try, because it looked helpful for the glideslope and HAC. And there is my main problem as a no-joystick-and-no-airplane-knowledge-orbiter-captain... For some strange reason I feel more familiar in outer space :lol:

 

[Cras]

for a space plane, ReA 1 to 1.2 degrees, Ant 90-100 degrees, Re-entry Alt 80 km

 

[Mythos]

for a space plane, ReA 1 to 1.2 degrees, Ant 90-100 degrees, Re-entry Alt 80 km

With those values in BaseSync I have again 3/4 orbit from deorbit burn to target, what is as mentioned before too shallow and leads to a skip-reentry.

With the BaseSync default values (that BaseSync calls made for earth) I get 1/3 orbit ahead. That is much too steep and I can't reach an AoA so that Aerobrake looks good, I'll always overshoot.

So here I still don't see how BaseSync and Aerobrake could be linked.

Also I can't find the point when to switch from Aerobrake to Glideslope. If I leave the path from Aerobrake in any way I won't come out near my target. But I have to change anything since Glideslope always says I'm not on path.

 

[Cras]

dont go by when Basesync tells you to de-orbit, go by what it says the dV is.

use that and plug it into Aerobrake to see what the result will be, then time your burn accordingly.

As for Glideslope, if you are using an XR-series vessel, I recommend only using it for horizontal situation, and stick with Aerobrake for the rest. That is how I do it.

 

[Tommy]

With spaceplanes like the XR series, getting the DEO burn at the "right" place is optional. I can land an XR-5 (assuming it's almost empty) in well under 10M from DEO to runway - or do the DEO burn a full orbit "early". At it's normal re-entry mass, about 18.5 is optimal (if re-entering from ISS).

I don't usually use BaseSync. The XR vessels have a LOT of cross-range, so why waste the fuel on a base alignment burn? If I'm bringing it in overweight, I'll make the alignment just to make the re-entry a bit easier.

The "easy" way is to just de-orbit 1/2 orbit before the target, and lower your PeA to about 50k. Then just use Aerobrake to determine the AoA and bank needed to reach target and ride it out. You'll "bounce" a little bit, but you son't ever be in any real danger of burning up. You can get rid of the bouncing by de-orbiting a bit close to the target - around 17.5M to 18M from target for a re-entry from the ISS.

 

[Wrangler]

With those values in BaseSync I have again 3/4 orbit from deorbit burn to target, what is as mentioned before too shallow and leads to a skip-reentry.

With the BaseSync default values (that BaseSync calls made for earth) I get 1/3 orbit ahead. That is much too steep and I can't reach an AoA so that Aerobrake looks good, I'll always overshoot.

So here I still don't see how BaseSync and Aerobrake could be linked.

Also I can't find the point when to switch from Aerobrake to Glideslope. If I leave the path from Aerobrake in any way I won't come out near my target. But I have to change anything since Glideslope always says I'm not on path.

Well... They are not actually linked. BaseSyncMFD serves 2 purposes in my reentries. Firstly, it tells me which orbit would be the best one for the Deorbit burn (i.e. with the lowest cross range to the target base). Just make sure that you type in the target base in the TGT text box. Secondly, I use it for calculating the the deorbit burn. Now since you are trying to avoid a skip Entry, just reduce the ANT Angle. something like 45-50 degrees (experiment with that). But keep the entry angle 0.5 to 1.15 degrees. anything more will be too steep. Anything less, will be too shallow. After the Deorbit burn, you will have to coast to the EI point. So switch to AerobrakeMFD and SurfaceMFD. Do make sure that you enter the target base in the TGT text box of the AerobrakeMFD, and click PG to get the graphical projections of your entry. Use that graph to manage the reentry profile, so you can avoid the pebble skipping the ground.

On the shuttle fleet (and I read someplace that also on XR5) you can try the AutoFCS to fly the whole deorbit, reentry and landing for you. Not much fun after a while, but it is a great way to observe a complete profile and take notes. Helped me understand the whole S-turn and roll reversal technique, and how to perform the TAEM to establish a good HAC. I am still refining my TAEM procedures during the manual reentries ( still mucking it up there). but that's the fun part. LEARNING!

Sorry for the Rambling.... But boy am I having fun these days...

 

[Cras]

yeah, there really is no reason to make a burn to make sure you pass RIGHT over your target base, unless you are landing on the moon or something else w/o and atmo.

For maximum cross range capacity, enter as shallow as possible. If you go for a steeper angle, your cross range will be diminished.

 

[Wrangler]

yeah, there really is no reason to make a burn to make sure you pass RIGHT over your target base, unless you are landing on the moon or something else w/o and atmo.

For maximum cross range capacity, enter as shallow as possible. If you go for a steeper angle, your cross range will be diminished.

Yes. But you get best results with a low cross range. I have found it easier to manage the approach with a cross range < 100KM from the target base. As for making a burn to adjust the cross range, you can do that if your spacecraft allows such extravagant use of fuel (e.g. DG). You generally don't have that liberty in the Space shuttle (not sure about the XR series. Those ships are still on my to-do list).