Typical youth of today
Too lazy to walk across to the podule and get the groceries in.
SpaceX today called off an attempt to berth its Dragon cargo capsule with the International Space Station after the, er, podule got a bit lost. It's fine, though: they'll try again on Thursday. The capsule, which was successfully launched into space on Sunday, was due to hook up with the orbiting science lab on Wednesday …
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"As a pilot it is sometimes better to accelerate and circle around than attempt a difficult landing."
This is sooooo true! After 50 some odd tries, and many visits to the hospital, I got clean away with the fighter jet in GTA V and when arriving at my friendly dessert aero puerto I had a "hard landing" and ruined the landing gear and the engine. That was it. Just a lovely hunk of polygons in the dirt. Next time I did a proper landing, and if it looks shaky then throttle up, flyover, and try again.
The Dragon capsule is hooked by a robotic arm once it approaches close enough and is then coupled to an airlock in the middle of the ISS. The Soyuz Progress capsules dock automatically at the far end of the station where they can transfer liquids and fuel as well as boost the ISS and raise its orbit by firing the service module's main engines. This means there's no need for one cargo capsule to get out of the way of the other to find a parking space. Usually though the mission controllers don't like two ships manoeuvering around the ISS at the same time so they'll probably prioritise one docking operation over the other.
I think the record for number of cargo and passenger ships at the ISS at one time was six, including a Space Shuttle as well as an ATV launched by ESA but none of them docked while the others were still in free flight near the station itself.
It would be interesting to know exactly what went wrong. There's nothing in the NASA release. A 'wrong' value in the software doesn't really say much.
Given that such guidance systems are essentially dealing with nothing but a bunch of velocities, it suggests that the capsule was moving at the wrong speed, or (due to a faulty sensor) at least thought it was. Not good. At least their supervisor processing spotted the problem and did the right thing.
It would be very interesting to know the flight history of their software. Was this version 'tried and tested' (they've sent Dragons to the ISS before), or has someone modified it recently?
Good luck on Thursday.
According to NASA TV, a wrong value about the ISS position was uplinked from the ground. So nothing wrong with the hardware or the software that was in orbit. I don't know where the wrong value came from; whether it was a typo, or someone not allowing for the 24-hour launch delay, or ground hardware.
Ah interesting! But that is a strange design I think. Clearly the spacecraft itself was capable of determining the relative position of the ISS, didn't like what it saw and bailed. If so, why does anything have to be uplinked from the ground?
Worse still would be if that value was due to a typo; allowing human error to play a part in a safety critical operation sounds back to front. Normally (airliners, self driving cars, trains, nuclear reactors, etc) the human is there to supervise the machine, not the other way round.
I don't know many details of the Space-X system, but I read elsewhere that the error possibly came from bad GPS value or calculation. Typically, medium range docking uses a sort of Differential GPS to compute relative distance and velocity. Possibly the distance and/or velocity suddenly changed by an amount outside of expected values.
In an earlier failure report that I read for Dragon, it said that the system failed from a Single Event Effect; some particle of radiation corrupted a value or signal, causing the system to trip. Normally critical space systems are designed to be immune to these types of event.
Big argument while trying to talk "her" into a tight parking spot.
"Right, now come straight back. NO!! I said straight back. Let's try again. Now come straight back. NO!! What did you turn the wheel for!! I said STRAIGHT BACK!!"
This went on for about 5 minutes until she eventually said "Well you do it then!" - so I did, in one go and without turning the wheel...
Prediction: arithmetic error due to poor choice of intermediate data type or lack of acumen when it comes to figuring out where to put the decimal point, to be covered up and reported as "transient firmware issue due to cosmic rays".
That, or someone used the wrong editor to open the python.spaceranger module and screwed up all the leading whitespace.
Thrrrrp! 8op 8ob 8op
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