Flight Question General Questions about orbiter (flight)

thumper235

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Ok, A week or so ago I posted how excited I was that I was finally able to make it to the ISS. I had this lingering thought that it was just pure luck. So last-night I thought why not try it again using the DG-IV. My first successful attempt was with the most excellent Ravenstar. Well, It was a success. I am going to stick with planes for now since it is has been said various times that is what noobs should use.

Now, Instead of congestion up the forums with multiple threads asking questions, I decided to write them down, organize them, and do this in one post. You all have been so helpful to me. I really cannot thank you all for the help you have kindly shared with me and given thus far.

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1) I take-off and try to maintain proper heading - I cant keep it perfect, but close enough. Say a heading of 136 is needed I will be 2-5 degrees off by the time I make my initial orbit. Using Autopilot for take-off also leaves me in the same ballpark maybe a little less. I have learned to use weight balance or trim tab to adjust my ascent angle. It seems using this keeps my flight much smoother and keeps me on course a little better.

Question - Is being off by 2-5 degrees normal? Would a real spacecraft/pilot have numbers like this?

Question 2 - If needed, Would you possibly share with me some ideas or techniques or ANYTHING to try out to help me on this part?
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2) Align planes with ISS - I have figured out how to use this, and how to correctly make my burns. I have also have a working understanding of how it ties into your takeoff heading being that its what corrects a "Bad" heading. The closer to your target heading you achieve equals more fuel saved by making less burns. I can make my Inclination right in the .02 -.05 range of my target depending on how long I want to work on it.

Question - When you personally do the ISS scenario how close are your numbers here? I want to be realistic with how this would play out for a real astronaut.


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3) Synchronizing my orbit with ISS. I understand the concept behind this. I can set my position to where I need to chase OR follow the ISS. This is where I loose any and all efficiency, but I can technically do it.

To modify whether I need to speed-up and catch the ISS or let the ISS catch me is by making a very small Pro/retro burn. There are 2 places I do this. When looking at your sync orbit display, You see the dotted line that runs through earth, each side of that line is where I make these small burns. At this point is where I become some sort of space-cowboy/cheater. Well, atleast I feel im cheating the system since Im not using it the way it was intended.

once I see the ISS and can make out its solar panels and other distinct features I make a small pro/retro burn to keep us "together". This will be the only burn I make that ignores the dotted-line rule I mentioned above. At this point I shred my RCS thrusters up trying to grab hold of the ISS.

Question - What is the easiest way I can learn how to use this more efficiently. For some reason I am having trouble with the tutorials on youtube.

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What I do in order

1) Take-off and try to keep heading
2) Align planes
3) sync orbit
4) turn on docking nav
5) Rape Rcs thrusters

My goals

1) learn and perform the ISS scenario like I know what im doing.
2) Re-enter earths atmosphere and land at KSC.
3) Take on the moon. 1)flyby and return to earth 2)land and return to earth
3) Mars with landing + return to earth
4) JUPITER BABY! visit any of her moons I can.
5) Go visit everyone else and to pick up my trophy at Brighton beach.

If I follow it in this order I think I should learn the skills needed to achieve my ultimate goal which is getting to Jupiter and being able to perform basic spaceflight.
 

Nazban

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1) Whenever I launch, Im always around the same 2-5 degrees off from the heading, that is alright, you cannot get it perfect, and even if you do, chances are that you will still have to do an alignment burn, so thats not a problem.
When I started off with orbiter, I used to always use Kill rotation when launching, makes it much easier, but as I started going realistic, I figured that its very hard to do keep on heading with a keypad, the best thing to use is a flightstick. When using a flight stick, keep movement at a minimum while aligned with your heading, and you should be fine.

2) I make my relative inclination to 0.00, On my first burn, I reach numbers close to that, but on my second burn, I use transnational thrusters to make it a perfect 0.00 degrees.

3) This is not easy to answer, personally I actually keep using different methods sometimes, when being realistic I just use either a pro/retro burn depending on relative positions, and once i get in sight i use transnational thrusters to dock, but most of the times I find myself needing to make the same burn like you mentioned, to keep both crafts together and not fly past it.

And I have to also say im impressed on what you've done so fast!! It took me weeks to properly dock to the ISS (without DG-IV programs :p) :cheers:
 

PhantomCruiser

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A few degrees of for me isn't unusual. But I can follow LaunchMFD and baby the ride up and get a really low (less than 0.3 if I pay enough attention).

Sync orbit can be tough sometimes. But I think the video Tex put together sums it up nicely. The trick is learning when the best time to start burning to match speed with the target (in your case, the ISS). As you are finding out, just because you can see it, doesn't always mean that the best time to drink up RCS fuel to get to it.

If I'm flying something like the Dragon (or a Soyuz) I try not to have such a huge altitude disparity between me and the station. For instance, if the station is at 350Km, I'll aim for and match the stations altitude (350) as my ApA.

After I've done this, it's time to tweak the alignment with AlignPlanesMFD.

I'll watch SyncMFD and as my DtMin gets below 100, I'll burn prograde (at Apa, I don't want my 'high point' altitude to change). Instead I'm bringing my PeA up. I'll do this several times until the difference between ApA and PeA are only 25-30 km (less is better). Remember if you have the stations altitude and your altitude matched at ApA, you will intersect with the station...

It seems as if this method takes "forever", but in only takes 5 or 6 orbits (maybe more), so string that out to 'real-life' and its only several hours, at best a half-day or so, depending on when the launch happens along the targets orbital track.

Eventually, it'll be time to burp the main engines a few times to truly match the stations orbit, at this point I'mm really just station-keeping, and it's a matter of using translation thrusters to line up and dock.

http://www.orbiter-forum.com/showthread.php?t=2055
Tex's video was a real help for me to wrap my head around SyncMfd. The DGIV or XR fleet can really make a station rendezvous and docking seem easy after a while. But I finally found that the DGIV has a docking autopilot (after about three years of docking without it).

edit - I think I got all my three letter acronyms straight. If I'm off, I hope you've understood the intent of what I was getting at...
 
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Ripley

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About syncing, I've recently found out, to my surprise, that if you start working early and constantly (read very often) on:

1) zeroing out RInc with rudders on ascent, and later with Norm+/Norm- burns;
2) carefully tuning Rendez-vous point altitude;
3) zeroing out DTmin;

Well, doing carefully these 3 things, Rendez-vous kinda "sorts itself out".

This is not the quickest method, and assumes nearly matching orbit altitudes, and very low Ecc.
When approaching target, speed will "magically" decrease by itself, and we won't need "chasing" it around, spoiling our intercept.
Give it a try, I was really impressed.
 

martins

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1) I take-off and try to maintain proper heading - I cant keep it perfect, but close enough. Say a heading of 136 is needed I will be 2-5 degrees off by the time I make my initial orbit.
What is the "proper heading"? The heading isn't an invariant parameter of your orbit, unless you launch east or west from the equator. If you try to stick to a heading of 136 degrees indefinitely you'll spiral towards the south pole.

Better to use the orbital elements (in this case, inclination and longitude of the ascending node) as control parameters.
 

Cras

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Rendezvous MFD is how I do my rendezvous. Depending on where the target is at the time of launch, I will set myself up in a higher or, more likely, a significanlty lower orbit. As I catch up, I will align the planes, then as I get closer still, raise the orbit higher and higher, until Rendezvous MFD springs to life, and I can use its guidance to approach the object at know how fast my velocity will be compared to the target.
 

TMac3000

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I do it by direct ascent. The trick here is that the vast majority of your trajectory will be suborbital; you won't actually reach a full orbit until you are close to the station.

1) While on the ground, pull up Synch Orbit and Map MFDs. Accelerate time until the station's ground track is passing over your base. Now wait until the station is the right distance behind you (don't let it pass overhead). This distance will be different depending on how long your ship takes to reach orbit. For the DG-IV and XR-2 it's 3200 km. For the XR-5 it seems to be about 3700 km. When the ISS is at that distance, take off and turn to either 042 or 132 depending on whether the ISS is on its northern or southern leg.

2) Proceed to orbit as normal with an apoapsis that matches ISS, but instead of circularizing your orbit, aim to match velocity with the station. Zero out your velocity, then turn toward the station and burn until you have a comfortable approach speed.

3) By now you should be within 600 km of the ISS. Tune your radio and watch the CVEL value on the Docking MFD. When this reaches 0, you have reached your closest approach. Zero out your velocity again, and burn toward the station again, setting a nice, comfortable approach speed.

4) Repeat step 3 until you are within 100 km of ISS, then switch to the IDS freq and approach as normal.

The above process takes me roughly 2 hours from liftoff to contact. The trickiest part is figuring out that takeoff distance. This takes a little trail and error, but I assure you it works quite well;)
 

thumper235

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Wow! Thank you all! This is a perfect example of the beauty of these forums and the people who empower them. Its really cool how through my adventures whether its building my first telescope, rocket, or this simulation how helpful and wanting-to-help the "space" communities have been. I hope once I get the hang of this I can give back to the community as well. This is good stuff.


Thanks alot everyone. I mean that. :thumbup:
 

Tommy

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I can offer a tip for getting low RInc during ascent. As Martin said, your heading will change - unless you launch from the equator at 90 degrees. If you launch from KSC, and try to maintain the same heading throughout the ascent, you will make the RInc worse, not better.

To a good low RInc, in a winged vessel like the XR-2, I use the following method:

1). Open AlignPlanesMFD and target the ISS. I want to take off just before the ISS's path crosses overhead, I find that launching at TN=300 works well for me. In order to be more efficient, I keep the speed down at first. I'll take off and throttle down to hold 200 m/s to 225 m/s and about 10 degrees climb while I turn to heading. I get the heading just right - and from then on I just keep the wings level. Once I'm on heading and level, I'll pitch up and throttle up for the ascent. I won't pay any attention to my heading, just keep the wings level until I'm going at least 4.5 km/s, then I look at AlignPlanes (AlignPlanes won't be of much use at lower velocities). If the Rinc is decreasing, I just keep the wings level. If it's increasing, or holding steady, I'll try banking to see which direction helps.

This gets me into orbit with no RInc, and syncing is just a matter of patience.
 

thumper235

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I did it! I did it! I did it like I knew what I was doing! SCORE!!!! haha! If you read my stats you might get a general idea of what I did wrong.

1) I did not wait for the ISS properly on the ground. This led to making a ton of ultra low orbits to catch up since it was almost on the other side of earth away from me by the time I made it to orbit. Much time was lost here.

2) I dont think I utilized my Scram engines efficiently enough seeing how much fuel was left over. I need to read about them a little more to figure out how to squeeze every drop of performance out of them, or perhaps learn how to use them correctly. Basically, I wait till I hit mach 4-4.5 and throttle them up.

3) I used the XR5 Vanguard for this run and did not realize the docking port was shuttle style. This made for a huge huge huge loss of RCS fuel and time. I got to the station mid-day and by to time night came I gave up and just tried to hang-out until the sun cam around again. As soon as got light I latched on.

1day 13:30 minutes mission time
35% main fuel remaining.
13% RCS remaining.
52% Scram fuel remaining.
APU 2660.

Its nice to know also that if need be in an emergency I can transfer fuel around a little bit from my main to RCS and so fourth. Its also so satisfying to know I can actually do this now without feeling like im cheating the system. Now its on the re-entry and learning to land at KSC and then to the moon. Good times! :thumbup:

@Martins - I am assuming you are the creator of Orbiter. Thank you so much for this. You have no clue how grateful I am and how much I appreciate what you have done for all of us. THANK YOU.
 

PhantomCruiser

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Nicely done, and yes, timing is everything.

As far as scram fuel goes, I'm generally around 45-45% left after getting to orbit, I domp scram fuel during my descent because I don't use scram engines returning home so it's just useless weight. 35% fuel on the mains is low, but you'll get better with practice. And you already know why your RCS fuel is so low.

You'll find there are as many opinions for deorbit/recovery as there are for acsent. And of course there's a video that might help you out (or at least get you close). Oceanic has a good one, it uses the DGIV but the procedure is essentially the same for the XRs, the attitude hold AP in the XR fleet is different, but not so much so that it'll cause you any heartburn. And you can find it here...http://orbiter-forum.com/showthread.php?t=8425
You'll need to get AerobrakeMFD and BasesyncMFD if you don't already have them, they are wonderful tools. Not essential to get the job done, just very nice to have.

Bringing an XR-5 in deadstick is still one of my favorite things to do in Orbiter, it just never gets old :thumbup:
 

ADSWNJ

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Nice thread, Thumper. It's interesting to see just how much of an artform these ascents and docking styles are. Vive la difference!! I fly the XR2 and XR5 most of the time, and getting max value out of the SCRAMs is something to really practice. You can fly the whole ascent by hand, but I try to bring in some autopilot assistance to help focus on the goal (i.e. getting to an ideal suborbit with the least amount of fuel burn), whilst letting the AP deal with wings level and pitch attitude. So ... take off ... drop on the speed hold AP at 200-225 m/s to roll to the right bearing (at say 3-4km alt), pitch up to 60-70 degrees and then throttle up to climb to 14-16km, then work to get the XR straight and level for 24km alt. The trick with the SCRAMs is to keep them breathing the right amount of air for as long as possible. You basically ignore worrying about going up, because you know with enough forward velocity you will reach suborbit (and then circularize to a full orbit at the APA). Rather - you want to climb and accelerate in a balanced way such that the scrams get fed enough rammed air to work efficiently, without keeping the ship too low in the atmosphere that you overheat the wings and over-ram the engine. Say 100-200 m/s ascent, or just a few degrees of pitch up will do it. Again though - art not science!

On RInc ... I try to get sub 1 degree. The more you let the AP's fly, the more you can supervise them to get to this level. On a manual ascent 2-3 degrees is usually more the ballpark.

On docking ... I think of it like reeling in a big fish. I want to have a perfectly aligned orbit on Align Planes (i.e. RInc 0.00 and the nice 90 degree between AN and DN shape from the final alignment puff of translation thruster to get there). I want to have a perfectly aligned AgP (argument of periapsis - i.e. where round the orbit the low point is). Do this by small prograde fwd or rev thrusts on the 90 or 270 degree MnA points of the orbit (i.e. half way round from Apo to Peri or Peri to Apo). This is important for docking with vessels in a non-circular orbit, so you are making an oval orbit to overlay right on top of theirs. Next, you want to be using Sync Orbit to align by Sh Apoapsis (which now overlays on the target apoapsis as well because of the AgP aligning). So you want to be scooting round under the target (say both ApA and PeA 100km or mor below the target, but above say 200km) until the orbits to closest approach get down to say 6 or 7 (Sync Orbit LEN = 18 to get a good list of orbits). Then get your ApA aligned, which will slow down your rate of catching because you are now in a bigger orbit. Than as Phantom says - bring up your PeA in steps until just 20-30km below the target. Each time, get to 3-4 orbits to closest, then raise the PeA, watching how the orbit times start to align. (e.g. if you are 40 secs faster on orbit, and you bump the PeA up closer, you will end up say 20 secs faster and now your closest orbit is say 6 away not 3). So it's fishing ... reel it in a bit, get closer, reel in, etc. I.e. if you were 10 orbits away and bumped it to be say 5 secs faster on orbit, you may need 50+ orbits to align, but if you do it with a binary chop - say 4 orbits out for a crude alignment, then 2 orbits out for a tighter one, then focus on getting DTmin to zero. Do all this, and your final burn to get on station will be sub 10 m/s and you will be 500m - 1000m from the target, in a beautiful orbit ready for docking.

I'm sure others would take pride in screaming in on an aggressive intercept, all guns blazing and dropping out of warp right onto the ship, but me - I want a smooth and precise approach and keep the fuel consumption as low as possible.

By the way - if you get used to the XR's thrust capabilities, then the STS shuttle comes as a big shock :). You have to treat it very differently, as the OMS thrusters are a lot less powerful. (i.e. a lot more realistic, I'm sure the STS fans would say!).

Happy orbiting, pilots!
 

thumper235

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@ADSWNJ Thanks for the figures on the scram engines. This actually might help solve my issue with using them for what they were intended. I have basically been taking off with mains at 100% get just a bit of altitude and knock back to 60% and then turning myself to the proper heading then throttle them back up to 100%. Its the altitude that like you have mentioned that is where I wasted the potential goodness they offer. I have been keeping my ascent of around 10-14 degrees. So by the time I get enough speed to engage my scrams, I am to high and hence the atmosphere is too thin to really get the use out of them. I am going to practice what you have said. Thank you for the figures. It gives me an idea on-the-fly of where I need to be.

On the Rinc that is an *AWESOME* idea. It will make is easier for me to view the ISS without having to press the up for down keys sliding my instrumentation up and down while in the cockpit. I get a little bit of (dare I say) anxiety when I have to race to flip a switch or make an adjustment. Anyways, you rock! :tiphat:


@PhantomCruiser Yes, I do have AerobrakeMFD and BasesyncMFD. HA! The funny part is YOU are the one that prompted me to get them sometime ago. I have lurked here for a very, very long time. On a side note, one of the weirdest things is there are a bunch of you here that I feel like I almost know because of spending so much time reading your posts. Its really cool listening to everyone's take on whatever the subject is at a given time.

The XR-5 is a tough one to re-enter and dock with. I have accomplished both now, but re-entry is by far a very pay-attention-intensive process. Its like my eyes are moving at the speed of light checking temps, attitude, etc etc. I still have not hammered out with any craft yet how to re-enter smoothly. I did once with the XR-2 Ravenstar and I *think* i did it right because I kept her nose at a 40 degree angle while hitting the atmosphere and not burning up, nor floating back up into space. For that instance, I somehow ending up off the middle coast line of South America heading east. If it wasnt for the fact I had very little APU fuel I could have probably cowboy'd my way home to KSC. I need to sit down watch other people re-enter to get a feel of how its being done and then take a serious approach to learning it. Also, MFD's and MORE MFD's!!!! :)

Also, I am flight stick shopping.
 

ADSWNJ

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I'm probably biased (Phantom too, I guess), but I love docking and reentry with the XR5 big bird. If you get into that really good alignment so you can slide up smoothly to the target, then visualize flying the ship into the docking corridor (i.e. intersect the docking HUD rectangles), then jump into the docking port view and of course be sure to set the docking RCS mode so it feels natural.

On the reentry - I see other pilots talking about bring her in at 1 degree slope, 80km interface, 30 ant. I typically come in at 0.7 slope, 80km interface, 40 ant. Use attitude control, and tweak the nose up and down in 0.5 degree increments to maintain your range to target (as shown on AeroBrake). Enjoy the ride!
 

Tommy

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ASWNJ made a good post about docking, doing it in several steps like that is a good way to minimize fuel use - it will help eliminate over-correcting so you'll save fuel that you would have used fixing those errors. Also, if you fly a more realistic craft such as the Shuttle, the low thrust of the OMS engines and tighter dV budget makes "faster" rendezvous impossible. With a lower thrust craft you need to have a low RVel or you won't be able to match velocities fast enough.

I actually "invert" the AgP, so that my Apoapsis is in the same place as the target's Periapsis - this is a bit more efficient than intersecting at the target's Apo. However, the difference in fuel use is so small you won't likely notice anyway!

There are lots of good threads here on how to optimize the ascent with an XR vessel, but you don't really need much fuel to sync and dock. As long as you are in orbit and have the planes aligned even 5% fuel is plenty.

To give a nutshell version of a good ascent profile, I'll break it down into four "stages".

1: Take-off and turn to heading. I described this earlier in this thread, keep about a 10 degree climb and keep the speed around 200 m/s.

2: Initial Ascent. Once you are on heading and wings level, throttle to full and pitch up. Adjust the pitch so that your Acc (lower left on SurfaceMFD) is close to zero but NOT NEGATIVE. On an XR-2 that will be 70 - 80 degrees, or 50 - 60 degrees in an XR-5. It will vary depending on cargo mass, etc. The goal is to get above 10k alt without increasing the velocity - keep it under 250 m/s. This is done to reduce drag losses - trying to go faster in that thick of an atmo is a waste.

At 10k altitude (as early as 8k in a heavily loaded XR-5) I'll trim down the elevator - at least 3/4 downward trim. I'll watch the VS, should stay around 200 or less - if it gets higher use more downward trim. You should begin to accelerate and break the sound barrier somewhere between 13k and 15k altitude. The goal is level flight at 22k - 24k Alt, then gain speed up to mach 3 in an XR-2 or mach 4 in an XR-5.

3: Scram ascent. Once you've reached mach 3 (or mach 4 in an XR-5) engage full scram and reduce main throttles as much as you can - but keep the ACC at about 5 m/s. Increase the climb rate gradually. As you gain speed you will be able to cut the main engines and still accelerate - and you will want a VS of around 200 m/s to avoid overheating. After 30k altitude, start slowly lowering VS down to around 100 m/s by 40k. Ideally, you will run out of scram fuel just as the engines begin to overheat - but up to 5% scram fuel remaining is fine if you aren't loaded heavy.

4: Establish Apogee. You should be over 60k -65k alt by scram shutdown, close the doors and engage mains. Keep a slow climb rate (about 75 -100 m/s) and watch your ApA. Once it hits the target for your parking orbit (ususally just over 200k) shutdown the engines. This should occur at around 75k altitude - still well with the Atmo. Keep an eye on your ApA - if it's climbing trim down, if it's dropping trim up, etc. Once you are above 100k the air is thin enough to ignore and you can go to 10x time accel.

5: Circularize. Nothing special here, just wait until you are close to your Apogee, orient prograde, and fire mains to circularize the orbit.


Tips: High AoA means high drag, so avoid using the stick after the first pitch-up. Using just elevator trim during the ascent will keep the AoA low. If you start to lose altitude even though you are at full upward trim it's fine - just keep full upward trim and you'll start climbing again as your speed increases. Keep the full up trim until your climb rate is back to at least 100 m/s. Watch your Dynamic pressure - it's a good clue as to how how much VS you want. I like to keep the DynP at around 20 Kp at first, letting it fall SLOWLY as I gain speed.

A similar profile works with non-scram gliders as well - but you want a bit more altitude during stage 3 to reduce drag a bit more (DynP target is about 15 kp) since we don't need to feed the scrams.
 

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I'm also a new user to Orbiter, and I'm having lots of fun. I have also realised that there is a LOT to learn. It's making my brain ache..... I've been practising with the DeltaGliderIV, watched Tex's video through a few times now and I think I'm starting to understand the principles of the physics involved. I wish I'd come across this years ago, the old brain cells aren't as good at absorbing new knowledge as they used to be!:hmm:
 

ADSWNJ

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I'm also a new user to Orbiter, and I'm having lots of fun. I have also realised that there is a LOT to learn. It's making my brain ache..... I've been practising with the DeltaGliderIV, watched Tex's video through a few times now and I think I'm starting to understand the principles of the physics involved. I wish I'd come across this years ago, the old brain cells aren't as good at absorbing new knowledge as they used to be!:hmm:

Too true, my friend. When you think you are anyway close to perfecting something, you get to the realization that you are now a total novice again in the next league up of professionalism! I could read posts like Tommy's all day - it's truly learning from one of the masters around these parts.

---------- Post added at 02:00 PM ---------- Previous post was at 01:37 PM ----------

ASWNJ made a good post about docking, doing it in several steps like that is a good way to minimize fuel use - it will help eliminate over-correcting {snip}

I actually "invert" the AgP, so that my Apoapsis is in the same place as the target's Periapsis - this is a bit more efficient than intersecting at the target's Apo. However, the difference in fuel use is so small you won't likely notice anyway!

{snip}

Tommy - loving reading your work here!

On the alignment (touching our Apo to the target's Peri) - I assume that in the end, our orbits will have the exact same angular momentum, so the fuel burn should be the same, unless you steal some of the target's energy.

Let me set up a quick example. Say you were docking with a target ("X") in a 300km x600km orbit, and we ("O") are in a 200km x 220km orbit. Aligning O-Apo to X-Peri, we would "reel in" towards a 300 x 300 orbit (e.g. final burn from 290 x 300 to 300 x 300). Now - in the say quarter to half orbit of docking, X is swinging up toward 600km alt, and we will need to constantly chase it. What I am trying to figure out though is: say we docked within 5 minutes of our Apo / X's Peri. At the instant before docking, we are still roughly in a 300 x 300 orbit, and X is 300 x 600. At the instant after docking, I assume we steal momentum from X to end up in a new conjoined 300 x 450 orbit? Else where would the energy come from to bounce us into X's orbit apogee.

Summary - gut feel to me says align the orbital elements perfectly to have the best time docking (less need to chase the orbital eccentricity), and not to steal any momentum. Pretty neat discussion though for first thing Sunday morning!

{snip}

1: Take-off and turn to heading. I described this earlier in this thread, keep about a 10 degree climb and keep the speed around 200 m/s.

2: Initial Ascent. Once you are on heading and wings level, throttle to full and pitch up. Adjust the pitch so that your Acc (lower left on SurfaceMFD) is close to zero but NOT NEGATIVE. On an XR-2 that will be 70 - 80 degrees, or 50 - 60 degrees in an XR-5. It will vary depending on cargo mass, etc. The goal is to get above 10k alt without increasing the velocity - keep it under 250 m/s. This is done to reduce drag losses - trying to go faster in that thick of an atmo is a waste.

At 10k altitude (as early as 8k in a heavily loaded XR-5) I'll trim down the elevator - at least 3/4 downward trim. I'll watch the VS, should stay around 200 or less {snip}

Tips: High AoA means high drag, so avoid using the stick after the first pitch-up. Using just elevator trim during the ascent will keep the AoA low. {snip}

Never thought about focusing on keeping acc close to zero sub 10km, but it makes complete sense. Trimming rather than ailerons is also something I'll need to try out. Thanks Tommy - new ideas here!
 

Tommy

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On the alignment (touching our Apo to the target's Peri) - I assume that in the end, our orbits will have the exact same angular momentum, so the fuel burn should be the same, unless you steal some of the target's energy.

Let me set up a quick example. Say you were docking with a target ("X") in a 300km x600km orbit, and we ("O") are in a 200km x 220km orbit. Aligning O-Apo to X-Peri, we would "reel in" towards a 300 x 300 orbit (e.g. final burn from 290 x 300 to 300 x 300). Now - in the say quarter to half orbit of docking, X is swinging up toward 600km alt, and we will need to constantly chase it. What I am trying to figure out though is: say we docked within 5 minutes of our Apo / X's Peri. At the instant before docking, we are still roughly in a 300 x 300 orbit, and X is 300 x 600. At the instant after docking, I assume we steal momentum from X to end up in a new conjoined 300 x 450 orbit? Else where would the energy come from to bounce us into X's orbit apogee.

Um, no. You have to match your velocity with the target's BEFORE you can dock - otherwise you'ld just smash into it. When you null the RVel during rendezvous, you are are matching the target's orbit - so you'd be in the 300km - 600km orbit before you actually docked.

I would start from a circular parking orbit of about 210km, and raise my Apo to match the target's Periapsis - same location, but a couple km higher. Then, at my new Apo, I would raise my Periapsis to sync at some future orbit. All adjustments will be made that way, at my Apo (be careful not to lower your PeA too much!).

As I approach the target I may use RCS translation to adjust my approach, and when I'm as close as I'm going to get I use the Docking HUD to null the relative velocity. From there it's just a matter of patiently moving in.

Summary - gut feel to me says align the orbital elements perfectly to have the best time docking (less need to chase the orbital eccentricity), and not to steal any momentum. Pretty neat discussion though for first thing Sunday morning!

It's more efficient to match the target's orbit at the target's periapsis. Remember - changes in the AMOUNT of your velocity should be made when you are closer to a gravity source - changes in direction are best made farther away from the gravity source.
 

thumper235

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Thanks Tommy!

Tonight has been the BEST so far. Everything just went really, really smooth. The ISS just floated up to me very gracefully and my numbers now reflect my improvement. I am now officially moving on to the re-entry. I do have some final questions relating to this ISS scenario that I will ask below. The questions are more basic, but left overs that I could use a little input on.


87.4% RCS
48.2% main
0% scram (Thanks again Tommy!)
78%-ish on the APU. <-- The APU its me forgetting to turn it off/laziness.

Question time!!!

Inclination - Suppose I have to change my inclination by 2 degrees. Whether I do the burn at 180km or 325km does it make a difference in the fuel needed to complete it?

Surface MFD questions
GS - Ground speed? My speed relative to sea level, right?
OS - Orbital Speed? My...????
TAS - True air speed???

Equatorial plane - I wiki's this and for some reason I can wrap my head around it. They even showed a picture. Can anyone break it down just a little bit for me?

Analemma - Please also break this one down for me.

Impulse - Its the force a rocket engine can produce per-second. Impulse It is represented by N or KN in math form?

APR - This is short hand in the orbiter MFD as apoapsis?


Which craft should I use to learn how to re-enter? Which videos and tutorials would you suggest for this?

As always, Thanks in advance!
 
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