Quote from: Jim on 01/11/2017 01:27 pmQuote from: Stan-1967 on 01/11/2017 03:52 amSTS did not go from orbit to landing site with no propulsion. The OMS engines delivered the impulse to direct STS to it entry interface corridor. This is analogous to F9's boostback burn. Wrong. The OMS just changed the orbit to one that intersected the atmosphere, so it is not analogous to the boost back burn.Sounds like Woody telling Buzz Lightyear he's not flying, but just falling with style.But what do you really think about the tools that could enable precision landing? You correctly pointed out the enabling technologies that STS used, will any of those have application to Mars EDL or other likely destinations?
Quote from: Stan-1967 on 01/11/2017 03:52 amSTS did not go from orbit to landing site with no propulsion. The OMS engines delivered the impulse to direct STS to it entry interface corridor. This is analogous to F9's boostback burn. Wrong. The OMS just changed the orbit to one that intersected the atmosphere, so it is not analogous to the boost back burn.
STS did not go from orbit to landing site with no propulsion. The OMS engines delivered the impulse to direct STS to it entry interface corridor. This is analogous to F9's boostback burn.
I'm a software engineer, just looking at the problem from where I am, docking is an easier SW problem than landing the F9 booster. Call it intuition, since you seem to accept that as valid.
Jim, I take your statement as a working assumption: "software is easy".If software is easy, how is orbital mechanics hard? Newtons laws are fantastically simple. You dont need fancy long term trajectory prediction (over centuries, which are complicated) for a rendezvous. So if software is easy and your computer knows the orbit of your target, the software can predict its position far enough into the future for a rendezvous and subsequent docking. The rendezvous procedure is also fantastically simple. Here is the pseudocode:1. Approach from a lower orbit2. Align orbital planes3. Raise your orbit slowly timed such that you approach your target from behind4. Initiate dockingFor the docking, the target docking port needs to provide a signal of some kind that you can target. Keeping stationary requires frequent adjustments using thrusters, but thats all software which is, as you say easy. So here is the pseudo code for docking:1. Align your spacecraft and the docking port in a defined state2. Approach the docking port within a defined trajectory envelope3. if envelope is violated, abort docking and go back to step 1.4. otherwise approach until dockedThis is also not very hard. trajectory prediction requires orbital mechanics. But thats software which is easy. So.. how is docking hard?From your proposition that software is easy and no other statement about the difficulty of the task, we arrive at the conclusion that docking is easy. Which contradicts your statement that docking is hard. So one has to go or you need to provide more information what exactly is hard here.Also, I want to reiterate my last request: Please state your metric that you use to measure difficulty. Its really the hinging point of this conversation. Unless we agree on the metric, we will never agree on the difficulty statement.
The idea that software is easy... Is wrong.
Also, I want to reiterate my last request: Please state your metric that you use to measure difficulty. Its really the hinging point of this conversation. Unless we agree on the metric, we will never agree on the difficulty statement.
computer knows the orbit of your target3. Raise your orbit slowly timed such that you approach your target from behindFor the docking, the target docking port needs to provide a signal of some kind that you can target.
I must have missed the uncooperative part in the past. Why do you assume an uncooperative target? Thats not done unless you try to attack something. Why is that even part of the conversation?
I must have missed the uncooperative part in the past.
Wrong. It wasn't controls or guidance that prevented it from long ago. It was the incorporation of Supersonic retropropulsion and engine throttling, and the use of many smaller engines that allow them to be used for landing an empty stage. Autonomous rendezvous with a non cooperative target is harder.
So Jim, you take a particular hard case that is very special which requires a dedicated mission of docking with an uncooperative target and compare it with a routine operation of landing the first stage? Why would you do that? A comparison with a routine docking operation i.e. the ISS would make much more sense.
Doesnt the ASDS or the landing pad qualify as an "uncooperative" target? It's stationary ok but it's not exchanging any data with the vehicle just like the ISS.For me the F9 landing is more than just the sw to get it there. Theres a lot of systems work gone into the vehicle to make this happen from attitude control, restartable engines, shielding and so on. All been done before in different ways but never the way to F9 does it.As an ex realtime process control sw head I think the F9 sw work is top notch. It's a difficult problem to solve and yes they have tuned it time and time again with their landings and perfected it , but still a difficult problem to solve.
It is part of the conversion because it is hard. "Uncooperative" means it doesn't have any interaction with the chaser spacecraft.
That is what autonomous robotic servicing spacecraft will have to do. They will have approach a spacecraft that is not designed for routine rendezvous and docking. It will have to use onboard sensors to find the target spacecraft and then will have to find an area such as the launch adapter as a mating point.
And the visiting vehicles have so many more control inputs...Those sort of differences are not "software", they are inherent parameters of the control problem.ISS may be non-cooperative, but it's certainly not trying to evade. Given its own very poor control authority, suppose it was cooperating, what exactly would it have done other than just hold 3 axis stable, and wait for the VV to take its time, line up, and then glide forward?
Quote from: Semmel on 01/12/2017 02:53 pmcomputer knows the orbit of your target3. Raise your orbit slowly timed such that you approach your target from behindFor the docking, the target docking port needs to provide a signal of some kind that you can target.I said an uncooperative target. No data is exchanged between vehicles nor its the target attitude known.3. Why? What says the docking adaptor is in that location
Wrong, the ability to fly autonomously from orbit to runway landing is actually more difficult than autonomous RTLS and hoverslam landing.