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Unmanned Spaceflight.com > All posts by a member| Posted on: Nov 20 2016, 02:47 AM | |
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Senior Member  Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497 
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QUOTE (PDP8E @ Nov 19 2016, 01:56 PM)  • When the altimeter read 2000 meters, the gyros reported -10m (below the surface) Gyros don't measure altitude, and as noted upthread, IMUs can't be used to determine absolute height above the ground. So this part of the story makes little sense. Let's just wait for the report and ignore media misunderstandings. |
| Forum: ExoMars Program · Post Preview: #233467 · Replies: 177 · Views: 225993 |
| Posted on: Nov 1 2016, 02:23 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (HSchirmer @ Oct 31 2016, 09:54 PM) perhaps part of the story here is that Mars' atmosphere has some major density fluctuations? That's always been a fact of life for EDL. It doesn't look to me like it affects the terminal part of landing, it mostly means that the time spent on parachute can vary by a significant amount. It's basically why you need the radar, you can't rely on absolute pressure sensing to figure out your altitude relative to the ground. |
| Forum: ExoMars Program · Post Preview: #233273 · Replies: 177 · Views: 225993 |
| Posted on: Oct 29 2016, 09:25 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (Gerald @ Oct 29 2016, 12:36 PM) According to this ESA site, the propellant has likely been MMH (monomethylhydrazine), and "MON" as oxidizer, a mix of nitrogen oxides. No, the lander was a monoprop system using only hydrazine (N2H4). http://spaceflight101.com/exomars/schiaparelli-edm/ Same thing with MSL. I wasn't able to find the phase diagram of hydrazine, but I would expect most of it to have evaporated under martian ambient pressure. |
| Forum: ExoMars Program · Post Preview: #233238 · Replies: 177 · Views: 225993 |
| Posted on: Oct 27 2016, 04:29 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (katodomo @ Oct 27 2016, 04:43 AM) There's always laser altimeters for altitude and doppler Lidar for relative velocity. Radar is an extremely robust and mature technology and the larger beam footprint and longer wavelength can be an advantage. The landing applications for lidar I know of are for terrain hazard avoidance, not altitude/velocity determination per se, for example https://www-robotics.jpl.nasa.gov/publicati...aejJGCD2002.pdf AFAIK, every successful Mars lander (and Moon lander, for that matter) has used radar. |
| Forum: ExoMars Program · Post Preview: #233189 · Replies: 177 · Views: 225993 |
| Posted on: Oct 26 2016, 08:50 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (Art Martin @ Oct 26 2016, 12:39 PM) Instead of using radar to decide altitude... You are reading way too much into that basically non-technical history. Radar is essential for Viking or any Mars lander that has to do anything based on altitude, as the altitude relative to the ground can't be determined any other way. |
| Forum: ExoMars Program · Post Preview: #233170 · Replies: 177 · Views: 225993 |
| Posted on: Oct 26 2016, 07:04 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (JRehling @ Oct 26 2016, 10:46 AM) Formal program verification, as the literature defines it, is not a part of any software development process that I've been around. I have a PhD in computer science and I develop flight software for a living (among other things) and I use whatever tools I can, including formal correctness. But I guess I'd agree that it's not common. QUOTE The software that was supposed to turn on radio receivers listening to two partially-redundant radio channels did not turn on one of the two receivers... My understanding is that this was user error (miscommanding) rather than a software failure per se. Software can be complex, and the simpler it is, the more likely it is to be right. Landing on Mars should not be that hard from a software perspective. |
| Forum: ExoMars Program · Post Preview: #233167 · Replies: 177 · Views: 225993 |
| Posted on: Oct 26 2016, 02:17 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (Gerald @ Oct 26 2016, 12:10 AM) Those event-triggered multi-threading systems are very hard to test and debug. A sensible designer would never use such a structure for a flight control application. There have been well-understood flight control algorithms in use for almost 50 years that can be tested. Note that Viking landed on Mars with a very simple computer the very first time. http://history.nasa.gov/computers/Ch5-6.html |
| Forum: ExoMars Program · Post Preview: #233162 · Replies: 177 · Views: 225993 |
| Posted on: Oct 26 2016, 04:00 AM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (Art Martin @ Oct 25 2016, 02:10 PM) From what I read the unit was not tested in actual flight conditions but instead simply by sending it simulated echoes. You don't subject your flight hardware to harsh conditions, you take an identical unit out for "qualification testing". IIRC, in the case of MPL, for example, this involved bolting a radar to an F-16 and diving it at the ground. There are limits to the fidelity of testing, but simulations are a key element. For landings many thousands of simulated landings are done to build up statistics on the distribution of behavior. With all that, MPL was doomed by a couple of missing lines of code that would have taken 5 minutes to write. The Genesis SRC crashed because its G-switches were installed backwards. Stupid mistakes happen. |
| Forum: ExoMars Program · Post Preview: #233153 · Replies: 177 · Views: 225993 |
| Posted on: Oct 25 2016, 06:49 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (JRehling @ Oct 25 2016, 08:58 AM) As a career software engineer, I doubt very much if either logical correctness or speed of execution are much of an issue here. Logical correctness is always an issue. As an unrelated example, MPL failed because of a lack of proper software debounce in the contact sensor that detected landing. I guess you can call that dynamics, but I'd call it a logical failure. At any rate, however you characterize them, software errors can be stupid and simple or extremely subtle or anywhere in between. If I had to make mistakes, I'd prefer to make subtle ones, but failure is failure and nothing much would surprise me in this case. |
| Forum: ExoMars Program · Post Preview: #233145 · Replies: 177 · Views: 225993 |
| Posted on: Oct 24 2016, 04:03 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (Sean @ Oct 24 2016, 07:44 AM) I will add my tuppence worth to Damia's argument... having a few extra images would do wonders for outreach... I think Damia's point is quite valid, not that there is much I can do about it. And there are some technical issues associated with how autofocus and autoexposure behave with the RTG in the field. That said, you can say that this would "do wonders for outreach" but the specifics are a bit lacking. Most media outlets can't do anything with a full 360 pan anyway and I'd say that MSL has been doing just fine with its press presence. |
| Forum: MSL · Post Preview: #233124 · Replies: 1206 · Views: 885304 |
| Posted on: Oct 24 2016, 02:03 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (vikingmars @ Oct 24 2016, 03:34 AM) But it's a pity that, with all the bandwidth available, they chose to miss taking some pics of the rover itself. You know, I used to think that, but when we did it that one time it was less interesting than I was expecting. Maybe all the selfies lessened the impact. |
| Forum: MSL · Post Preview: #233120 · Replies: 1206 · Views: 885304 |
| Posted on: Oct 24 2016, 03:32 AM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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The time in the file name is an SCLK value and drifts around in a way tabulated by the NAIF group http://naif.jpl.nasa.gov/pub/naif/MER/kernels/sclk/mer1.tsc . According to the quick Python program I just wrote (below) this time corresponds to 2016 OCT 19 14:51:27. But your conclusion is right. I'm not sure how the imaging times for the MER imaging were commanded but this seems late. CODE import math import sys from spice import * furnsh("naif0001.tls") furnsh("mer1.tsc") t0 = scs2e(-253, sys.argv[1]) print "t0", t0, et2utc(t0, "c", 0), et2utc(t0, "isod", 0) |
| Forum: ExoMars Program · Post Preview: #233117 · Replies: 177 · Views: 225993 |
| Posted on: Oct 23 2016, 09:42 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (neo56 @ Oct 23 2016, 11:10 AM) Here is my take. My gosh, was the sun really this close to being in the field? Somebody on the ops team needs a good talking to.  |
| Forum: MSL · Post Preview: #233114 · Replies: 1206 · Views: 885304 |
| Posted on: Oct 23 2016, 08:23 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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These images were likely not autoexposed, but you're ignoring the fact that these are frame transfer cameras and would show artifacts with anything moving in the scene, which would probably lead to some kind of streaking for fast-moving objects regardless of exposure time. That said, the team looked at these images and said they saw nothing but cosmic-ray hits, so I'd say leave it at that. |
| Forum: ExoMars Program · Post Preview: #233111 · Replies: 177 · Views: 225993 |
| Posted on: Oct 21 2016, 04:13 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (tanjent @ Oct 21 2016, 07:20 AM) But because I just can't help myself, I am curious to know if any of the non-photographic science data will be made public in real time... can we look forward to any interim hints about what is being learned? I know of no plans to release any science data "in real time". I would expect that as is always done, at regular intervals and if anything interesting is learned, there would be a press briefing or press release, just like there was a couple of days ago. |
| Forum: Juno · Post Preview: #233076 · Replies: 130 · Views: 149915 |
| Posted on: Oct 21 2016, 02:15 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (Gerald @ Oct 21 2016, 01:28 AM) I barely dare to ask, whether JunoCam has been powered on between October 15 and 19, and whether it has taken images during this time... Nope, we didn't get to the first image before the s/c safed. |
| Forum: Juno · Post Preview: #233070 · Replies: 129 · Views: 127797 |
| Posted on: Oct 20 2016, 03:13 AM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (PaulM @ Oct 19 2016, 09:35 AM) I have read that this is why opportunity's European made instruments have an analogue interface and not a digital interface to the main computer. This is not only OT but pretty nonsensical. As an example, the foreign instruments on MSL (RAD, part of Chemcam, and REMS) are not analog interfaces. The digital interfaces may not be publicly documented, and ITAR is often invoked, but they are certainly not secrets within the project. IMHO the ESA EDL demonstrator is as much about politics and nationalism/regionalism as it is about technical issues, and I have been working on space missions with international participation since the mid 80's. |
| Forum: ExoMars Program · Post Preview: #233040 · Replies: 177 · Views: 225993 |
| Posted on: Oct 19 2016, 05:49 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (PaulM @ Oct 19 2016, 09:35 AM) Entry descent and landing technology is classified because of its relationship with ICBM technology. While there is some truth to this (for "classified" read "covered by ITAR"), there is plenty of open-literature information about US Mars EDL systems. |
| Forum: ExoMars Program · Post Preview: #233024 · Replies: 177 · Views: 225993 |
| Posted on: Oct 15 2016, 04:29 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (Explorer1 @ Oct 14 2016, 10:58 PM) And on the bright side, it gives Juno more time away from the radiation belts, which is probably good for the final lifespan.... There's very minimal science possible away from perijove, so a longer lifespan has no real value on its own. |
| Forum: Juno · Post Preview: #232986 · Replies: 130 · Views: 149915 |
| Posted on: Oct 15 2016, 05:09 AM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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https://www.missionjuno.swri.edu/news/next-jupiter-pass "Mission managers for NASA’s Juno mission to Jupiter have decided to postpone the upcoming burn of its main rocket motor originally scheduled for Oct. 19." Some scrambling here today to generate an imaging sequence for the PJ2 pass. |
| Forum: Juno · Post Preview: #232980 · Replies: 130 · Views: 149915 |
| Posted on: Oct 12 2016, 08:06 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (JRehling @ Oct 12 2016, 11:51 AM) At the very least, the announcement is late... I suppose that's all there is to say about it… Yes, that's all there is to say about it. https://spaceflightnow.com/2016/09/07/nasa-...e-insight-woes/ "the head of the agency’s science division said this week NASA will still approve development of at least one new solar system probe in December." |
| Forum: Exploration Strategy · Post Preview: #232948 · Replies: 145 · Views: 312255 |
| Posted on: Oct 12 2016, 03:30 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (Gerald @ Oct 12 2016, 06:16 AM) Context map for PJ1, southern hemisphere... That's really nice. It would be more scientifically useful if you presented it in a standard cylindrical map projection (no duplication) and defined the coordinate system (central longitude, which longitude system, latitudes planetographic or planetocentric, etc.) And identifying which images were used would be helpful. |
| Forum: Juno · Post Preview: #232943 · Replies: 129 · Views: 127797 |
| Posted on: Oct 1 2016, 11:34 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (Tom Tamlyn @ Sep 30 2016, 02:48 PM) To my eye the test image looks less fuzzy than the actual final image... There's no reason to think that their ground unit is focused identically to the flight unit, especially for distances well inside the requirements. |
| Forum: Rosetta · Post Preview: #232848 · Replies: 390 · Views: 451387 |
| Posted on: Sep 30 2016, 06:46 PM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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QUOTE (xflare @ Sep 30 2016, 01:44 AM) I haven't been able to find the Dates and Times of the upcoming Perijove close approaches, does anyone have them? These were accurate at one time, I haven't checked them lately but they should be pretty close. Times in UT, obviously. CODE orb[ 0] = "05-JUL-2016 02:47:38" orb[ 1] = "27-AUG-2016 12:51:20" orb[ 2] = "19-OCT-2016 18:11:07" orb[ 3] = "02-NOV-2016 17:52:29" orb[ 4] = "16-NOV-2016 16:54:46" orb[ 5] = "30-NOV-2016 15:52:21" orb[ 6] = "14-DEC-2016 14:49:58" orb[ 7] = "28-DEC-2016 13:47:35" orb[ 8] = "11-JAN-2017 13:59:37" orb[ 9] = "25-JAN-2017 12:57:12" orb[ 10] = "08-FEB-2017 11:54:47" orb[ 11] = "22-FEB-2017 10:52:21" orb[ 12] = "08-MAR-2017 09:12:44" orb[ 13] = "22-MAR-2017 08:10:19" orb[ 14] = "05-APR-2017 07:07:53" orb[ 15] = "19-APR-2017 06:05:27" orb[ 16] = "03-MAY-2017 06:17:26" orb[ 17] = "17-MAY-2017 05:14:57" orb[ 18] = "31-MAY-2017 04:12:29" orb[ 19] = "14-JUN-2017 03:10:03" orb[ 20] = "28-JUN-2017 03:40:40" orb[ 21] = "12-JUL-2017 02:38:12" orb[ 22] = "26-JUL-2017 01:35:46" orb[ 23] = "09-AUG-2017 00:33:19" orb[ 24] = "23-AUG-2017 00:08:07" orb[ 25] = "05-SEP-2017 23:05:44" orb[ 26] = "19-SEP-2017 22:03:21" orb[ 27] = "03-OCT-2017 21:00:55" orb[ 28] = "17-OCT-2017 20:35:43" orb[ 29] = "31-OCT-2017 19:33:14" orb[ 30] = "14-NOV-2017 18:30:45" orb[ 31] = "28-NOV-2017 17:28:16" orb[ 32] = "12-DEC-2017 17:02:53" orb[ 33] = "26-DEC-2017 16:00:20" orb[ 34] = "09-JAN-2018 14:57:50" orb[ 35] = "23-JAN-2018 13:55:18" orb[ 36] = "06-FEB-2018 12:52:47" orb[ 37] = "20-FEB-2018 11:39:44" |
| Forum: Juno · Post Preview: #232833 · Replies: 129 · Views: 127797 |
| Posted on: Sep 28 2016, 02:25 AM | |
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Senior Member Group: Members Posts: 2559 Joined: 13-September 05 Member No.: 497
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http://www.asteroidmission.org/wp-content/...tember2016.jpeg QUOTE On September 22, 2016, two weeks after launch, the OSIRIS-REx spacecraft switched on the Touch and Go Camera System (TAGCAMS) to demonstrate proper operation in space. This image of the spacecraft was captured by the StowCam portion of the system when it was 3.9 million miles (6.17 million km) away from Earth and traveling at a speed of 19 miles per second (30 km/s) around the Sun. Visible in the lower left hand side of the image is the radiator and sun shade for another instrument (SamCam) onboard the spacecraft. Featured prominently in the center of the image is the Sample Return Capsule (SRC), showing that our asteroid sample’s ride back to Earth in 2023 is in perfect condition. In the upper left and upper right portions of the image are views of deep space. No stars are visible due to the bright illumination provided by the sun. Credit: NASA No stars are visible because 1) the exposure time was too short to see any, and 2) Stowcam is focused on the SRC and stars would be way out of focus. Oh, and thanks for the image credit.  |
| Forum: OSIRIS-REx · Post Preview: #232796 · Replies: 70 · Views: 177588 |
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