Question Thorton's Soyuz FG/U 1.2 - reaching the ISS, how?

[TG626]

Has anyone successfully reached the ISS using the included scenarios? I find that reaching orbit before 3rd stage burnout is hit or miss, and when I do get to orbit I am WAY below the ISS...

Is something off with this addon or is there a tutorial for getting Soyuz to the ISS (there are tons for things like that for the DG, but Soyuz doesn't have that kind of fuel to spare...)

 

[diogom]

I've made it the ISS with these scns. It's not much different from using other spacecrafts. All you need to do is be a bit more careful with fuel, and know that the engine is less powerfull than say, a DG. And the autopilot should always get you to orbit.
Being below the ISS, that's normal. That's what happens with real Soyuzes actually.
Now a tutorial, I think I can't do that, sorry.

 

[TG626]

I've made it the ISS with these scns. It's not much different from using other spacecrafts. All you need to do is be a bit more careful with fuel, and know that the engine is less powerful than say, a DG. And the autopilot should always get you to orbit.
Being below the ISS, that's normal. That's what happens with real Soyuzes actually.
Now a tutorial, I think I can't do that, sorry.

Well, at least this is a STEP in the right direction :thumbup:

So... it's normal for Soyuz/Progress to be in a lower orbit when the last stage burns out?

Thinking about it, I might be able to figure this out if the "Sync Orbit" MFD showed a list that was 35 entries long (lol)

That's the trouble, all the stuff out there is based on the UBER powerful DG and trades lots of fuel/thrust for time in getting to the ISS - I'm trying to do this in at least a semi prototypical manner.

Is there any place where I can see a DETAILED break down of a soyuz-iss flight plan?

 

[N_Molson]

A big part of the job is to find a proper launch window. When the last rocket stage burns out (Block I), you should have ideally a Rinc < 0.1° . Over 0.5° is very bad, you probably aren't going to make it. You can use LaunchMFD or use the included scenarios for that.

As for the lower orbit, you are going to take advantage from that. On a 220x200 km orbit, you accomplish your orbit faster than the ISS, at roughly 350x350, does. So you have to wait you are "under" the ISS. As in real life, this can take up to 3 days (depending of the ISS position when you launched, the worst case is when it is just behind you, which tends to happen often).

Because of various perturbation, your Rinc is going to increase during those 2-3 days. Don't let it grow too much, and make regular corrections.

From SyncMFD, check DTmin. You want it < than 0.1

If you manage to keep Rinc and DTmin < than 0.1, you are on the right path. You will meet the ISS at a few kilometers of distance. Then cancel the relative velocity (V-) on the Docking MFD, and go for docking !

Oh and keep the joystick for the docking manoeuver, and use the keyboard with the RCS "impulse" modes (preferably 0.05s and 0.1s). This saves a lot of fuel.

And when you are waiting, press K to let the autopilot track the Sun and load the batteries !

 

[TG626]

As for the lower orbit, you are going to take advantage from that. On a 220x200 km orbit, you accomplish your orbit faster than the ISS, at roughly 350x350, does. So you have to wait you are "under" the ISS.

...snip...

If you manage to keep Rinc and DTmin < than 0.1, you are on the right path. You will meet the ISS at a few kilometers of distance. Then cancel the relative velocity (V-) on the Docking MFD, and go for docking !

Ok, I'm with you on this right up until "at a few kilometers distance". If I'm in a 200 x 220km orbit and the ISS is in a 350 x 350km orbit, then the closest I can possibly come to it is 130km. That's a whole lot more then a few.... somewhere along the line I'd have to raise my orbit to be around 350km, or at least my apogee. So the question to me is, where/when do you do that? I'd assume that the orbit is raised little by little on each orbit until it comes close to the ISS orbit at around orbit # 35.

I tried waiting until I was a few orbits from overtaking the ISS and then raise my apogee to intercept the ISS orbit, only to find that I was going WAY too fast and I shot past the ISS. You can't waist impulse like that with a Soyuz.

ARRG! It's so frustrating...

 

[lindemherz]

Patience, man, patience. Go back to Go Play on Space (http://orbiter-forum.com/showthread.php?t=79), read the tutorial, do the tutorial, learn the basics ideas behind rendezvous until you feel comfortable with them. Then check that non-spherical gravity box in the Orbiter launcher menu. Be ready to improvise a bit on the fly because with non-spherical gravity is not as easy anymore, and then practice with the uberpowered Delta Glider.

Really practice.

Practice, practice, practice, practice coming in from higher orbits, from lower orbits, from behind, from the front, practice like a madman until you can do it with a three burns, a percent of fuel, just using the thrusters, coming smooth as silk (well, not literally, but almost). When you're able to pull that off, you'll find out that it's the same doing it with the Soyuz and its soft engines. The only differences will be your launch and burn times - the mechanics are the same, the techniques are the same.

And then you'll pull it off.

Of course, that's why astronauts train and train and train again, to be able to do it in real life with a couple of hundred metres of dV. After thousands of hours in the sim, of course rendezvous is gonna be a piece of cake.

 

[N_Molson]

Well, if you manage to come at 130 km from the ISS, here are a few rules to follow :

- Don't think you'll be able to cover those 130 km with the SoyuzTMA engine. You haven't enough Dv for this kind of "cowboy" manoeuver.

- When you are at those 130 km, try to get the same Apoapsis & Periapsis than the ISS.

- From there, four cases :

1) You are 130 km behind the ISS. You need to (slightly, less than 10km) reduce your Periapsis so that you will orbit a little faster than the ISS. At some point, you should catch it up and get in the 10 km zone, which is the goal.

2) You are 130 km ahead of the ISS. This time, raise your apogee, and you will orbit slower. Same conclusion than above.

3) You are 130 km on the "lateral" axis (Normal or AntiNormal). This is a problem of plane alignment. Use Align planes MFD to fix things up.

4) You are 130 km above or below the ISS. Synchronisation problem. It is where Sync Orbit MFD is very useful (after all, Orbit MFD in target mode is enough to close up from the ISS). You need to find an Intersection.

Then, when you are in the "10 km from the ISS zone", use Dock HUD / MFD to get the vector you need to match speed with the ISS, displayed as "V+" and "V-". Point "V-", then engage full thrust until it nears 0.

A sidenote about this : with the tank full, the SoyuzTMA has 390 m/s of DeltaV (to make it simple, it means that you can change your orbital velocity by 390 m/s by performing a prograde or retrograde burn). If you get a "V-" vector of 100 m/s, this means you are going to use about 1/4 of the tank to bring it to 0. From there you should roughly have a null relative velocity. It's time for a "Starwars-like" approach, where you basically aim at the ISS and perform a short burn. Correct the approach vector with RCS linear. Note : if you accelerate from 10 m/s, you'll need to brake from 10 m/s, so you burn for 20 m/s of DeltaV...

And remember that, as a safety procedure, you should keep a strict minimum of 250 kgs of propellant for the deorbit burn (BO jettisonned or not). So there is little margin for error.

Edit :

I find that reaching orbit before 3rd stage burnout is hit or miss

Cryogenic fuel. The R-7 uses Kerosen (the fuel) and Liquid Oxygen (LOX, the oxydizer that allows the fuel to burn). LOX is very very cold, around -190°C. So, it can't be kept in a tank for a long time : it boils quickly as the temperature in the tank slowly raises (the tank is well isolated, but there are limits to this). When enough LOX has boiled off, the rocket will not be able to reach orbit. This means you made the fuelled rocket waiting on the pad for 1 day or 2, which is bad. To fix this, you can simply use the scenario editor shortly before launch, and fill the tanks of ALL the stages (Bloks A, B, V, G, I + the core launcher).

 

[TG626]

Thanks for that last bit, I didn't know these effects were modeled...

FWIW - fuel effeciency not withstanding, my usual accuracy is in the 5-15km range....

My problem isn't really doing the docking, it's having enough fuel to DO the docking...

Best mission so far was 18% left in the tanks once docked with the ISS, not enough to come home....

There also seems to be a great difference between the "4 min de-orbit burn" and Thorton's stated "lower your periapsis to around 60km" for reentry, but I'll get to that later....

 

[Krikkit]

I have one scenario, can't remember which, put me right behind the ISS every time. I can see it on screen as a few white pixels gliding in front of me after third stage cut off.

 

[N_Molson]

18% might be just enough if you jettison the BO before the deorbit burn (less mass need less power). Or if your Periapsis is < 120 km, you can expect a quick orbit decay by aerobraking (the problem is, that there is no way to predict where you will land).