my own way of doing reentry timing(is it correct?)

communist

Resident Crazy Person
Joined
May 14, 2010
Messages
209
Reaction score
0
Points
0
Location
Peoples Republic of Kazmia
i have a specific way of doing the timing for the reentry burn,
1:get to orbit using your own ascent or an autopiliot
2:wait a few orbits until your orbit plane passes near target base
3:eek:rient retrograde and fire retrograde when your bearing indicator says 90 degrees
4:reentry slope MUST BE -2 degrees(in the DGIV)
5:reenter and land.
is this the wrong way to do this??? if so leave a comment to propose another way
 
Last edited:

Tex

O-F Administrator
Administrator
Retired Staff
Tutorial Publisher
Joined
Oct 16, 2007
Messages
6,574
Reaction score
67
Points
123
Location
Houston
Website
youtube.com
If you're landing at the Cape in Florida, the easy way for me is to wait until my orbital plane is near the base and burn retrograde as I'm crossing the west coast of Australia. I'll simply burn retrograde until PeA comes down to 56k on the Orbit MFD.

EDIT - This works for the DeltaGlider, DGIV, XR2 from an altitude around that of ISS. For the space shuttle I do the same, but burn a little sooner since it is so massive with little thrust.
 

Mojave

60% Ethanol
Moderator
Addon Developer
Joined
Apr 6, 2010
Messages
1,647
Reaction score
132
Points
78
Location
Somewhere, but not here.
Landing at the Cape, I usually burn retrograde over the Indian Ocean, it usually turns out right. landing at Edwards, I burn a little behind the Indian Ocean.
 

communist

Resident Crazy Person
Joined
May 14, 2010
Messages
209
Reaction score
0
Points
0
Location
Peoples Republic of Kazmia
If you're landing at the Cape in Florida, the easy way for me is to wait until my orbital plane is near the base and burn retrograde as I'm crossing the west coast of Australia. I'll simply burn retrograde until PeA comes down to 56k on the Orbit MFD.

with that in mind could you try out my method,for my flights to orbit it works quite well
 

Mojave

60% Ethanol
Moderator
Addon Developer
Joined
Apr 6, 2010
Messages
1,647
Reaction score
132
Points
78
Location
Somewhere, but not here.
If you are asking both me and Tex, I can do it tomorrow. I am engaged in a different activity right now.
 

mc_

New member
Joined
Jan 22, 2010
Messages
342
Reaction score
0
Points
0
Location
South-Western Siberia
Usually performing retrograde burn at a half orbit before the base, and then making several "jumps" off the atmosphere to loose speed slowly. Works well (tested on XR), even no flames duaring re-emtry.
 

Izack

Non sequitur
Addon Developer
Joined
Feb 4, 2010
Messages
6,665
Reaction score
13
Points
113
Location
The Wilderness, N.B.
If you're landing at the Cape in Florida, the easy way for me is to wait until my orbital plane is near the base and burn retrograde as I'm crossing the west coast of Australia. I'll simply burn retrograde until PeA comes down to 56k on the Orbit MFD.

EDIT - This works for the DeltaGlider, DGIV, XR2 from an altitude around that of ISS. For the space shuttle I do the same, but burn a little sooner since it is so massive with little thrust.
Hey, thanks Tex! With that simple advice I was able to make my first completely successful realistic (relatively) reentry on Earth, just a few minutes ago! Spot on Canaveral in the DG-IV. :thumbup:

Yes, it's taken me this long to get around to it :p
 

Tex

O-F Administrator
Administrator
Retired Staff
Tutorial Publisher
Joined
Oct 16, 2007
Messages
6,574
Reaction score
67
Points
123
Location
Houston
Website
youtube.com
Usually performing retrograde burn at a half orbit before the base, and then making several "jumps" off the atmosphere to loose speed slowly. Works well (tested on XR), even no flames duaring re-emtry.

Very true, done this before myself, but where's the fun in that? :) I love pushing the limit sometimes for super quick reentries. We're talking red heat shield all the way to the runway.. haha!


Izack said:
Hey, thanks Tex! With that simple advice I was able to make my first completely successful realistic (relatively) reentry on Earth, just a few minutes ago! Spot on Canaveral in the DG-IV. :thumbup:

Yes, it's taken me this long to get around to it :p

Happy to help!
 

Tommy

Well-known member
Joined
Aug 14, 2008
Messages
2,019
Reaction score
86
Points
48
Location
Here and now
Rather than burning when the bearing is 90 degrees, the burn should be made when you are the right distance from the base you want to land at. For most vessels, from the ISS's altitude, around 17.2 M is about right (and this is about over the west coast of Australia). If you are higher, de-orbit sooner. If you are lower, de-orbit later. De-orbit burn should lower your PeA to about 50k, this should give a re-entry angle of about 1.2 degrees.

Note that this is pretty flexible. De-orbiting on the opposite side of the planet is fine, and if you use AerobrakeMFD you should have a nice, slightly "bouncy" re-entry that doesn't overheat a DGIV or XR. On the other hand, you can d-orbit a DGIV (no cargo - minimal fuel) 6.5M from target, with a PeA of -1000k (re-entry angle about 6.75), and survive if you are good at heat managment. (HINT: Use an AoA of 20 degrees until VS is about -50 m/s, then increase to maintain about -80 m/s descent.)

The key thing is that your de-orbit burn timing should be based on distance-to-target, NOT bearing.

I should add that the distance also varies a bit depending on the vessel. The stock DG and Shuttle make maintaining a high AoA very difficult, so a longer re-entry at a lower AoA works better for them.
 
Last edited:

ddom2006

New member
Joined
Nov 12, 2009
Messages
155
Reaction score
0
Points
0
If you're landing at the Cape in Florida, the easy way for me is to wait until my orbital plane is near the base and burn retrograde as I'm crossing the west coast of Australia. I'll simply burn retrograde until PeA comes down to 56k on the Orbit MFD.

EDIT - This works for the DeltaGlider, DGIV, XR2 from an altitude around that of ISS. For the space shuttle I do the same, but burn a little sooner since it is so massive with little thrust.

Ya mean I've been burning up hours of my life doing complicated manual re-entries all this time? Typical of me :rofl:. Will try your method shortly :thumbup:
 

insanity

Blastronaut
Donator
Joined
Jun 22, 2009
Messages
1,194
Reaction score
106
Points
63
Location
Oakland, CA
I use the deorbit mode of Basesynch and clean it up with aerobrake, but doing it purely manually, I do what Tex does.
 

ddom2006

New member
Joined
Nov 12, 2009
Messages
155
Reaction score
0
Points
0
Used Tex's method, burned up first two times due to hitting the atmosphere far too hard and fast, came in for a third time slower and at a less hard angle of attack and skirted probably a little too slow because I landed short of White Sands by about 200miles (roughly, going on speed...)
 

Tommy

Well-known member
Joined
Aug 14, 2008
Messages
2,019
Reaction score
86
Points
48
Location
Here and now
You don't say what you are flying, but I assume it's a DGIV or XR something. The key to avoid burning up is to keep the descent rate at around 80 m/s or less once you are below 65k altitude. If you are heavily loaded, use a lower descent rate, etc.

Ending up on target is harder, it takes a lot of practice to learn how fast you should be going at any given distance from target. You'll want to be within 75km of the runway by the time you hit 1km/s, at about 20k altitude.AerobrakeMFD makes this MUCH easier by showing you where you will end up if you maintain your current AoA and bank, and how fast you'll be going when you get there.
 

ddom2006

New member
Joined
Nov 12, 2009
Messages
155
Reaction score
0
Points
0
Apologies, It's been a 22 hour day already, tis getting to me somewhat :lol:. Indeed, It was a DGIV (Well... Three of them.) I burned up so much fuel getting my speed down after undocking from the ISS on my first attempt I ended up going deadstick apart from RCS thrusters into re-entry and burnt up pretty fast, 2nd attempt I hit the atmosphere sideways and it hit me back, 3rd attempt I levelled out at 18k, bounced around the lower atmosphere trying to keep the heatshield cool enough and aiming for White Sands, I at least managed to land the 3rd one, if off target :cheers:.
 

Skookum

New member
Joined
Apr 8, 2008
Messages
39
Reaction score
2
Points
0
Reentries are awesome. It took me a while to master a foolproof reentry procedure for the XR / DG IV. But after sorting out the right combination of MFD's and workflows, I can now land at any base from any orbit of 1000KM or less successfully EVERY TIME.

Here's a fairly detailed outline of the procedure:

First you need the following MFD's:

[ame="http://www.orbithangar.com/searchid.php?ID=2139"]Aerobrake[/ame]

Base Sync
[ame="http://www.orbithangar.com/searchid.php?ID=2763"]Glide Slope[/ame]



If using the XR2/XR5 I also like to edit the Preferences CFG and increase the maximum autopilot bank and pitch angles to 85 degrees (also handy for other atmospheric maneuvers not covered here).

Outline:

1. Starting in a roughly circular orbit of any altitude between ~200 KM and 1000 KM we conduct a burn normal to our orbit while using Base Sync MFD so as to place our flight path directly over our chosen landing site at least one full orbit in the future.

2. Precisely one half orbit (in Base Sync) before passing over the landing site begin a full thrust retrograde burn using main engines until Perapsis altitude equals zero.

3. Activate Aerobrake MFD and target your landing site. Hit PG and PRJ to bring up the reentry map. As you approach entry interface (~90 KM) activate the attitude hold/reentry autopilot and adjust your angle of attack (AOA, not pitch) to place the end of your predicted flight path on your landing site as displayed in Aerobrake MFD (~35-37 degrees ballpark). As you descend, continuously monitor and adjust AOA as necessary to keep the end of your flight path on target. This is the longest phase of the reentry.

4. At around Mach 8-7 activate Glideslope MFD on both screens. Hit NB/PB until desired landing site is displayed. Monitor altitude/speed (Alt/Spd line graph, not the 6 columns of numbers) on one screen and horizontal (HAC) alignment (Az) on the other. The altitude/speed profile is optimized for the space shuttle, but is close enough to be useful with the XR/DG. Now use your vessel's slope indicator to help you stay on the yellow altitude line. Speed (the green line) will take care of itself as long as you maintain the correct altitude profile. Remember increasing AOA will steepen your descent and vice versa.

5. At around Mach 2 you should be approaching the HAC. Reduce your AOA to nearly zero. Replace the Altitude/Speed graph screen with Surface MFD in IAS mode. Adjust your vessel's slope angle to intercept and maintain a 20 degree descent throughout the HAC as displayed by the glideslope indicator on the right side of the HAC alignment screen (Glideslope MFD). Use air brakes to maintain 190-200 M/S IAS.

6. As you approach the end of the HAC the runway should appear in front of you. Disengage autopilot, preflare, dump the gear and land normally.




Do's and Don't's:

- DON'T use time compression after activating the autopilot. YOU HAVE BEEN WARNED. :nono:

- DON'T forget to configure your ship for reentry (IE stow the radiator). Activate your airfoil surfaces.

- DO set up your screens in advance. You can preselect the desired base in Glideslope MFD and Aerobrake MFD well before you need it. This reduces your workload later on. Also, preselect your airspeed mode in Surface MFD (IAS) and tune your navaids. Having the HSI in ILS mode as you roll out of the HAC and line up with the runway is handy.

- DO monitor your AOA, flight path prediction, and descent rates closely. The XR autopilot gives you much more control over your AOA (0.5 degree increments). I highly recommend practicing reentries in that vessel. A little goes a long way, especially up high near entry interface.

- DO practice and have fun!!!:thumbup:
 
Last edited:

Tommy

Well-known member
Joined
Aug 14, 2008
Messages
2,019
Reaction score
86
Points
48
Location
Here and now
I burned up so much fuel getting my speed down after undocking from the ISS on my first attempt I ended up going deadstick apart from RCS thrusters into re-entry

It shouldn't take much fuel to de-orbit, a couple percent at most. You only need to lower your PeA below about 70k (Aim for 50k - 60k) and then you shouldn't need mains, just RCS to hold atitude.

In a re-entry from the ISS, you shouldn't burn up above 65k (70k for a lunar direct return), but you'll need to have slowed down by the time you hit 64k altitude. It's crucial to have your VS under control by the time you hit 65k. After that, just try to maintain a steady VS of around 75 - 100 m/s depending on fuel and cargo load. Even with full fuel and cargo (way over "max recommended" mass) you can have a descent rate as high as 40 m/s - if your AoA is around 35 - 45 so you are getting enough negative ACC. If you are under the 19??? kg recommended re-entry mass, 80 m/s of negative VS is fine. Watch the DGIV's full auto re-entry, it holds about -80 m/s rather than react to hull temps (and that's why you need to de-orbit correctly to use it!).

Focus on VS and VACC. Keep the VACC small (under 3 m/s if possible) and try to hold a steady descent rate. The DGIV is only adjustable in 5 degree increments, so either alternate between "too much" (and a negative VACC) and "too little" AoA (and a positve AoA). You can also use bank to help maintain a low VACC, just alternate between left and right bank to stay generally on target.

Re-entry is difficult, and you should be proud that you can even survive one. The trick is to know that you don't have direct control over the hull heat - it's affected by the VS versus the ACC (both being negative, hopefully!). You don't have direct control over VS, either. You do have control over VACC, by changing AoA or bank.

This means there is a real lag between Action and Result. If you wait until you are almost burning before you change the AoA, by the time the AoA changes the VACC which changes the VS which changes the heating, it's too late.

My first focus during re-entry is on keeping VACC as low as possible, then on keeping the VS where I want it, and only occasionally look at the hull temps.
 

Skookum

New member
Joined
Apr 8, 2008
Messages
39
Reaction score
2
Points
0
My first focus during re-entry is on keeping VACC as low as possible, then on keeping the VS where I want it, and only occasionally look at the hull temps.
Good advice
 
Top