NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: LADEE Moon Probe Puzzle
From: Derrick Young
Date: 2013 Sep 16, 13:08 -0400
From: Derrick Young
Date: 2013 Sep 16, 13:08 -0400
First, To Fred and others, I apologize for this being a long post. If not relevant, please delete. Peter, You ask a good questions. I don't know what NASA is doing now with the radar tracking data. I know what was done 40 years ago when we were launching SCOUT missiles from Wallops Island, Vandenberg and San Marco Kenya as well as the early shuttle launches from the Cape. There was always a projected gravity turn track that we wanted the launch to follow to get payloads into orbit. We had "dead bands" marked on either side of the launch track that would serve as the boundary layers for the range safety officers to consider separating the capsule and destroying the missile. When SCOUT program was finally shutdown, it was the most successful launch vehicle in the history of NASA. Three solid propellant boosters and optional 2 liquid upper stages (5 total). It had various add-ons to include the strap-on booster rockets for the first and second stage to increase payload capacity. And there plans to use SCOUT as the Inertial Upper Stage (later known as the IUS) for launches from the Space Shuttle, but that did not materialize. NASA and the Air Force opted for a new platform. Anyway, the SCOUT did launch a number of missions that very similar orbits to the LADEE moon probe. Just not the hoopla, because that was normal business back then. Yes, the craft that was built as the IUS did perform automated cellnav. It had to because knew where it was when the Shuttle disconnected the data feed (that included a time and position update), but there were no updates between the disconnect from the shuttle and the time the IUS woke up to determine the amount and direction of drift in the intervening 45 minutes between the disconnect and the wake up, when the Shuttle was moving away to a safe zone. The IUS's "wake up" triggered the unshuttering a telescope on the horizontal axis and begin a slow rotation around the horizontal axis looking for a target star (actually a star of specific brightness with a specific star field around it). If found, it would orient on that star (move it to center field) and then begin a slow rotation to locate the next star in the sequence. If the IUS did not find a star that it recognized, it would stay in the same plane and turn about 45 degrees to the right and rescan. It would repeat this process until found the set of stars needed to locate it's starting position. And it would continue until it had sufficient star sets located so that it's position could be calculated. Then based on knowing where it is as well as the desired end point (final orbit desired or interplanetary mission programmed in). The IUS would calculate the best method to get there using the least fuel. It would send a radio signal that it was ready to start, shortly thereafter initiate the assigned task. I know because I worked on the SCOUT program from 1974 to 1978, the Space Shuttle and IUS programs from 1978 to 1980 (five on board computer systems, each programmed differently, three of which had to agree for an action to be taken) and the IUS (again multiple computers on board, had to agree for an action to be taken). Lots of fun very cutting edge for the time it was done. Unfortunately, it is very different from the programming that is done now. Back then, we were heavily constrained by memory, timing, processor speed and I/O. Now my tablet has more power than all of the computers in the Shuttle or the IUS combined, and definitely more than any of the analogue computers in the SCOUT. But I would not trade that experience for anything in the world. If nothing else, I learned how to properly design and program, making use of every machine instruction and memory location out there. So be happy with the small position error you are seeing. Practice will improve your technique. Derrick “We are not what we know but what we are willing to learn." Mary Catherine Bateson, American writer and anthropologist -----Original Message----- From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Peter Monta Sent: Saturday, September 14, 2013 9:30 PM To: Young, Derrick CIV (US) DeCA HQ LEIP Subject: [NavList] Re: LADEE Moon Probe Puzzle ________________________________ Nice result! Is it likely that this 1.7 nmi disparity is estimation error from the photos, or could it be actual deviation of the rocket from the published track? I'm not sure I'd entirely trust a table in a press kit; is high-precision tracking data made available for these NASA launches after the fact? It brings to mind Jim Lovell's joke that the NASA mission controllers should download his navigation state vector, generated autonomously on-board from sextant observations, rather than use the one computed on the ground (which was always used in practice). The ground controllers replied "touch ". Cheers, Peter : http://fer3.com/arc/m2.aspx?i=125135