-
#60 by Barley on 25 May, 2022 18:08
-
Absolutely. The programmers would hate whoever made them do it. “Just solve it in software” LOL. They hate that.
As a programmer I can say we don't hate solving problems in software. Solving problems in software is our thing. What we hate is being told to solve problems in software at the last minute, without any resources and without a description of what the problem is. Or problems like melting tires -- very hard to solve in software; we did manage to cut it in half, but it really needed a chemist (or a new buyer).
-
#61 by Jim on 25 May, 2022 19:33
-
Explain why.
7200 sets of files to manage. 7200 Monte Carlo runs on the trajectories. 7200 runs on the SIL. 7200 trajectories to verify. -
#62 by Herb Schaltegger on 26 May, 2022 00:08
-
Explain why.
7200 sets of files to manage. 7200 Monte Carlo runs on the trajectories. 7200 runs on the SIL. 7200 trajectories to verify.
So Jim, let me ask you: do you know or have an opinion why SpaceX hasn't upgraded F9 avionics to support RAAN steering on ascent? Is it because they don't generally need it? Or because the use of sub-cooled LOX and the desire to hit a target bulk mean temp for oxidizer loads preclude the flexibility RAAN steering might gain them in longer launch windows? Or something else? -
#63 by ccdengr on 26 May, 2022 00:46
-
do you know or have an opinion why SpaceX hasn't upgraded F9 avionics to support RAAN steering on ascent?
I'm not Jim and this topic has drifted rather far from the Psyche specifics (which is fine, since it is a SpaceX thread) but I'd say it's because they haven't needed it and better is the enemy of good enough. Delta II had only instantaneous windows and worked fine for planetary missions (there we could get two windows per day, usually, by reloading parameters.)
-
#64 by Robotbeat on 26 May, 2022 01:49
-
This... doesn't sound beyond SpaceX's capabilities? We've been running monte carlo runs, trajectories, etc, for decades. Since the 80s, computer power (as well as memory capability) has increased more than 1,000,000 fold (for a given cost). SpaceX runs these calculations in an automated manner already (according to people who ought to know), they would not have to babysit each one.Explain why.
7200 sets of files to manage. 7200 Monte Carlo runs on the trajectories. 7200 runs on the SIL. 7200 trajectories to verify.
Again, the programmers would hate it; it'd need to be validated, etc. And frankly, this is probably not the best way to do it (ULA doesn't do it this way). But this is most certainly not beyond SpaceX's capabilities.
(Appreciate the response, BTW.)
-
#65 by ccdengr on 26 May, 2022 01:59
-
In my experience, reloading parameters would be a tedious and error-prone way to do this if you had more than a few sets. Rockets that have this capability simply perform the needed calculations on board. If SpaceX wanted to do that, I'm certain they could, but avoiding unneeded frills is just good systems engineering. Add more features, add more testing, add more error modes, etc. KISS.7200 sets of files to manage. 7200 Monte Carlo runs on the trajectories. 7200 runs on the SIL. 7200 trajectories to verify.
This... doesn't sound beyond SpaceX's capabilities?
-
#66 by Jim on 26 May, 2022 16:07
-
L
SpaceX runs these calculations in an automated manner already (according to people who ought to know), they would not have to babysit each one.
verification is not automated. People still review the data.
Launch vehicles don't carry that much memory.
also, an issue is managing the differences in the all the trajectories.
Other vehicles that have the capability to do RAAN steering, do trajectory checks at every minute and launch only on the minute but they only have one software load.
-
#67 by abaddon on 26 May, 2022 16:20
-
This begs the question; why did Lockheed (or ULA) implement it in Atlas V? And when? (And or Boeing/ULA for Delta IV, I know there were some changes made to adopt unified avionics at some point, so perhaps it came from the Delta side).do you know or have an opinion why SpaceX hasn't upgraded F9 avionics to support RAAN steering on ascent?
I'm not Jim and this topic has drifted rather far from the Psyche specifics (which is fine, since it is a SpaceX thread) but I'd say it's because they haven't needed it and better is the enemy of good enough. Delta II had only instantaneous windows and worked fine for planetary missions (there we could get two windows per day, usually, by reloading parameters.) -
#68 by ccdengr on 26 May, 2022 16:37
-
This begs the question; why did Lockheed (or ULA) implement it in Atlas V? And when?
I don't know, but this topic was covered rather extensively in https://forum.nasaspaceflight.com/index.php?topic=41982.0 and this is just a rehash of many of those points. Atlas II, Shuttle, and Apollo could do yaw steering.
-
#69 by abaddon on 26 May, 2022 17:28
-
Thanks for the link. I thought Falcon 9 can do "yaw" steering and often does, it is "RAAN" steering (dynamic trajectory?) that is lacking? Perhaps I am confused.This begs the question; why did Lockheed (or ULA) implement it in Atlas V? And when?
I don't know, but this topic was covered rather extensively in https://forum.nasaspaceflight.com/index.php?topic=41982.0 and this is just a rehash of many of those points. Atlas II, Shuttle, and Apollo could do yaw steering.
StackExchange has a link about RAAN steering: https://space.stackexchange.com/questions/55468/how-do-raan-steering-increase-the-launch-window that may or may not be good/useful. -
#70 by Newton_V on 26 May, 2022 23:18
-
Example of RAAN steering (coincidentally with a yaw maneuver that has nothing to do with RAAN target):
No RAAN steering case:
Just look at the red ground track only. Because of a flight azimuth constraint, and a lower target inclination than the azimuth allows, the vehicle yaws left (when allowed) to get to the inclination. The ground track will look identical for launch any time of day. You just wait for the correct time of day to get the desired RAAN of your orbit. Orbit will always be 200 km circ at 65 deg for example. If customer has a tolerance requirement of 0.1 deg, the launch window will be essentially instantaneous. If the requirement was +/- 7.5 deg, then you have about an hour window. No RAAN steering needed.
With RAAN steering:
If a customer still has the 0.1 accuracy requirement, the launch vehicle (LV) can utilize RAAN steering to increase the window (to get more launch opportunities that day, due to weather, anomaly resolution, etc), or sometimes a customer might have the longer window requirement (for the same reasons), and still want/require the 0.1 deg tolerance. In this case, you still determine the window optimal launch time that gets the RAAN you want (the red track), but now the vehicle is targeting this inertial plane. If you launch earlier (Earth hasn’t quite rotated around enough), the ground track will look like the purple plot. If you launch later, the olive track. The vehicle still goes to the same 200 km @ 65 deg orbit, the difference being WHERE you inject in the orbit (lat, long, time from liftoff, etc). The flight software only works for this period of validity that the flight software parameters were designed to. You can launch any time from window open to close. Any second, fraction of a second. Whatever. When you see launches only every minute, or 5 minutes, those are operational decisions, and have nothing to do with the LV capabilities. It just makes life easier for the customer and their ops for post-SV separation.
Atlas has had this capability going back to the Atlas II days. Titan IV had it as well. Delta IV did when common avionics came along.
One other note: You can do “psedo” RAAN steering, by just having discrete, optimized cases, at specific intervals, every 5, 10, or 30 minutes, etc, but then this requires uploading at new flight software parameter set throughout the launch window. Delta has done this. I believe Falcon might or might not have.
-
#71 by matthewkantar on 26 May, 2022 23:32
-
Would RAAN steering ever put the drone ship out of landing range?
-
#72 by Joffan on 27 May, 2022 15:54
-
Would RAAN steering ever put the drone ship out of landing range?
That seems possible, but unlikely.
As I understand it, RAAN steering is trying to hit a plane in sidereal coordinates, so Earth coordinates are essentially ignored (hence "possible"). However most of the steering to selected orbit for Falcon 9 is done by the second stage (when it is not an orbit achievable from direct launch azimuth). That of course means the booster would already be headed back to its chosen landing site by the time significant launch-time-dependent steering started. See OneSpeed's assessment of Falcon second stage steering from launch data. -
#73 by Newton_V on 27 May, 2022 15:55
-
Would RAAN steering ever put the drone ship out of landing range?
Begin the RAAN steering in upperstage flight. Costs more performance, but solves one issue. -
#74 by Jim on 27 May, 2022 21:06
-
And even further back, Gemini XII used lots of yaw steering, since they were rendezvousing with a target launched 90 minutes earlier. From the Gemini 12 mission report
Radio guidance and not inertial -
#75 by Jim on 27 May, 2022 21:10
-
Bumping this old thread, because I believe we've just seen Falcon 9 fully demonstrate yaw steering capability. The SAOCOM 1B launch involved dog leg maneuvers in both first and second stages, followed by an RLTS landing. Does this mean that, given sufficient prop margins, that some instantaneous launch windows could be expanded?
doglegs are not the same as yaw steering. -
#76 by Jim on 27 May, 2022 21:12
-
This is yaw steering
-
#77 by Jim on 27 May, 2022 21:18
-
From the MAVEN launchMSL had instantaneous windows, 5 minutes apart, all the way through the almost 2 hour launch window. Are you saying all of these had the same azimuth? If so, why? It's definitely giving up performance. What's the corresponding benefit?
They were not instantaneous windows. It had one continuous window at the same azimuth. They just scheduled launch attempts every 5 minutes. This was for down range tracking and spacecraft acquisition.Quote"For MAVEN, we've got a two-hour launch opportunity every day," said Jim Sponnick, ULA's vice president of Atlas and Delta programs. "And within those two hours, we have an opportunity to launch once every five minutes. It's those opportunities each day over the launch window make up those 1,000 trajectories. It's fairly consistent with how we have designed, developed and validated trajectories and mission designs for previous missions to Mars."
So you have one opportunity, each five minutes, each with its own trajectory. If you miss one, you wait for the next. That's the very definition of a sequence of instantaneous launch windows. Now if you want to claim it's due to tracking, and not the rocket, that's one thing. But for whatever reason, ULA implemented a sequence of instantaneous launch windows.QuoteThe flight profile from liftoff to Centaur MECO-1 were the same for all times and days.
So you are saying the first stage has a continuous window, so you can launch the first stage at any time you want, and it will work perfectly. I'd agree with that. Unfortunately, if you don't pick a time that is also compatible with the second stage working correctly, your mission will fail. Strangely enough, customers want launch windows where everything will work - first stage, second stage, tracking, sunlight, etc. So the mission launch window is the AND of all these constraints. In this case, it's a sequence of instantaneous windows.
Wrong, it is a continuous launch window that they choose only to launch on certain times for tracking and spacecraft acquisition. The launch vehicle still can launch at any second and there is no change to the software load. The only thing is done is just picking the launch time and starting the timing so it arrives on the planned interval. The space craft has done its analysis for those specific times and can setup tracking antennas for the expected trajectory.