Would a handheld GPS work on the International Space Station? - Page 1
Forum section: electronics / general

author: cvanc
author_rank: Frequent Contributor
timestamp: August 20, 2018, 02:33:44 am
content: Title says it all; would a consumer handheld GPS unit work accurately on-board the ISS?To put it another way, what is the maximum altitude that GPS actually works at?

author: @rt
author_rank: Super Contributor
timestamp: August 20, 2018, 03:25:21 am
content: The max altitude depends on the manufacturer, and they will also have a maximum velocity. and no... much lower altitude than ISS.

author: hamster_nz
author_rank: Super Contributor
timestamp: August 20, 2018, 03:43:47 am
content: The GPS signal is still there, as the satellites are in orbits at about 21,000 km, far higher than the ISS.Software the limitations on speed and velocity within the receiver would stop them from working, but this is a political not technical issue.As a technical issue, the added Doppler from being in orbit would cause the GPS receiver to fail to acquire and track satellites correctly - a ground based receiver is only designed for only +/- 5kHz of Doppler shift away from the nominal frequency. This not only affects the tracking loops within the receiver, but also the bandwidth requirements of filters and antennas.

author: rdl
author_rank: Super Contributor
timestamp: August 20, 2018, 04:24:28 am
content: I thought at one time there were laws that limited the altitude and speed at which GPS could work. Maybe that's not true any more and maybe it didn't apply everywhere.

author: Brumby
author_rank: Unknown
timestamp: August 20, 2018, 04:40:30 am
content: That's a legislative and political matter - but one that will (I think still) limit what consumer devices are allowed to do.While there may be some interesting challenges, I imagine you could get a GPS receiver to work in the ISS ... but it won't be an across the counter purchase at a Walmart.

author: james_s
author_rank: Super Contributor
timestamp: August 20, 2018, 04:52:42 am
content: With the ubiquity of cheap Chinese GPS modules I'm surprised there still exist any artificial limitations on GPS performance. The random vendors clearly have no ethical qualms about breaking laws of other nations so I can't imagine them caring the slightest bit about laws regulating the performance of GPS receivers. Our authorities can't seem to make a dent in the massive influx of obviously counterfeit parts so I wouldn't have thought that would be a barrier.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 20, 2018, 04:54:06 am
content: While admitting nothing I will comment that at least some models of GPS stop working in the neighborhood of 200 MPH.In addition to all of the difficulties mentioned above with using a handheld GPS, the space station is that it is basically a large aluminum container with a very few windows and with large conductive wings swooping about it. I would think that lack of signal would be a problem most of the time.

author: Brumby
author_rank: Unknown
timestamp: August 20, 2018, 05:06:00 am
content: I'm sure signal acquisition could be addressed. The orbital velocity of around 7.66 km/s would be a challenge, though.

author: hamster_nz
author_rank: Super Contributor
timestamp: August 20, 2018, 05:40:35 am
content: Quote from: Brumby on August 20, 2018, 05:06:00 amNot as hard as getting the active antenna out of the window and stuck onto the roof.I've got a little software project that you could do the rest... would just have to increase the searched bandwidth, and relax some of the tracking loops.https://hackaday.io/project/20965-full-stack-gps-receiver

author: JS
author_rank: Frequent Contributor
timestamp: August 20, 2018, 08:32:17 am
content: Quote from: james_s on August 20, 2018, 04:52:42 amThe limitations are imposed in the silicon, cheap Chinese won't roll their own silicon design, rather use somebodyelse's design which already has the limitationbuilt into it. Every serious gps receiver designer would comply with such regulation as there's not much point having a design which can't get certified.Mil specs receiver designs are probably much more rigorously protected against getting into such markets...Also, I doubt the CN government would want such devices around for under $5 in ready to use modules, so they might put some eye on that, even if they care nothing at all about western regulations.JS

author: Howardlong
author_rank: Super Contributor
timestamp: August 20, 2018, 08:57:39 am
content: Yes, it would, but as others have said there are limitations on commercial chipsets marketed in the US based on altitude, speed and/or acceleration because of their potential use in military applications (e.g., ICBMs).It's not too hard to find devices that work, ISTR Zarlink had an uncrippled chipset at some stage.It's also possible to roll your own GPS receiver with enough pizza and caffeine. I did some work with a HAB and rocket team from Cambridge University who rolled their own GPS in their spare time over the period of two weeks, that's impressive work.AMSAT also had a GPS on their AO-40 spacecraft. As it was led by AMSAT, they allow experiments on board that have their results made public, indeed it's pretty much a prerequisite to be taken as payload on an AMSAT spacecraft. AO-40 had an apogee well outside GPS MEO constellation, and it was an experiment to see how well GPS would function in this scenario. A few of my colleagues wrote this up their findings here:https://ntrs.nasa.gov/search.jsp?R=20020079110

author: Howardlong
author_rank: Super Contributor
timestamp: August 20, 2018, 09:13:42 am
content: I almost forgot about PCSAT, a LEO, orbiting above the ISS. I ran one of the command stations for it. That had a GPS on board, you can read about it herehttp://www.aprs.org/pcsat.html

author: David Hess
author_rank: Super Contributor
timestamp: August 20, 2018, 11:00:29 am
content: Quote from: rdl on August 20, 2018, 04:24:28 amThe US restricts exports of GPS hardware via ITAR which among other things includes restrictions on velocity and altitude. Some manufacturers interpreted this to be both velocity and altitude and some interpreted it to be velocity or altitude. Even without acquisition and locking problems, something in orbit would exceed both so it would not work with commercial hardware.

author: Zbig
author_rank: Frequent Contributor
timestamp: August 20, 2018, 11:49:54 am
content: I have tried using my smartphones' GPS on commercial flights several times during the years (differrent smartphones with stock, unmodified software) successfully. I was able to read both the aircraft's position and speed (in excess of 800 km/h) no problems. And don't worry, they were in Flight Mode each timeEDIT:To make my point clear, I was referring to the speed limit, not to suggest that if it works on an airliner, it'll be fine on ISS.

author: Howardlong
author_rank: Super Contributor
timestamp: August 20, 2018, 12:44:06 pm
content: Quote from: hamster_nz on August 20, 2018, 05:40:35 amHere are three methods:(a) Use an existing port, somenice pictures of how this is achieved here.(b) Autonomous unit mounted outside the ISS, e.g.http://www.aprs.org/pcsat2.html(c) Add a new module with the antennas pre-installed, e.g., the ESA Columbus module, which has apair of patch antennasthat I had a small involvement with.All of these needed an EVA.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 20, 2018, 02:52:12 pm
content: Quote from: Howardlong on August 20, 2018, 12:44:06 pmAll of these push the idea of handheld pretty hard.

author: LaserSteve
author_rank: Super Contributor
timestamp: August 20, 2018, 02:56:39 pm
content: The small Iranian LEO sat had a Rockwell Jupiter timing grade GPS on board it. It was clearly visible in the picture the Iranians released. It is one of my favorite boards, so I recognized it. As it was probably made before ITAR tightened up on personal GPS, my bet is it worked... I have a few of them in a drawer, but I'm short on modified missiles and LOX to try the experiment.I cannot see an engineer on such a high profile mission using a board known to be confused by Doppler or using known restrictive software on board.Edit Crass comment about Engineers dealing with angry Mullahs with Swords and not getting their "fix" removed .Steve

author: David Hess
author_rank: Super Contributor
timestamp: August 20, 2018, 08:17:48 pm
content: Quote from: Zbig on August 20, 2018, 11:49:54 amThe old ITAR restriction was 60,000 feet altitude and 1,000 knots so commercial flights should not be a problem but some receivers had issues anyway; my Garmin receivers always worked. Many users successfully used civilian GPS receivers on high altitude balloon flights but it depended on how the manufacturer interpreted the ITAR rules. Some GPS receivers quit if the maximum altitude *or* speed was exceeded and some quit only if both were exceeded so those worked fine on balloon flights.

author: David Hess
author_rank: Super Contributor
timestamp: August 20, 2018, 08:31:28 pm
content: Quote from: LaserSteve on August 20, 2018, 02:56:39 pmAs a recall, those early GPS units had separate mixed signal and digital ICs so it was possible to either reprogram them to ignore the restrictions or use the mixed signal receiver with your own processor.

author: james_s
author_rank: Super Contributor
timestamp: August 20, 2018, 09:03:23 pm
content: I have a hard time believing that no Chinese companies produce GPS receiver silicon. Certainly huge volume of other state of the art ICs are produced there.Now I've never had an opportunity to try using a GPS in a very fast moving vehicle so I don't even know if they will do that now or not. Someone else's comment of one working in an airliner suggests that at least some of them will.

author: JS
author_rank: Frequent Contributor
timestamp: August 20, 2018, 09:19:48 pm
content: I'm not saying there's no chineese silicon GPS receiver, I'm guessing there's no chinise silicon gps development, they just copy other designs by bigger companies that are certifiable GPS receivers. Developing a GPS IC is not trivial and development is more expensive than production, cheap CN market is based on saving development cost by using somebody else's design.JS

author: cdev
author_rank: Super Contributor
timestamp: August 20, 2018, 09:39:17 pm
content: I sincerely doubt if there are not Chinese companies making GNSS receiver HW, as they have made their own GNSS sats, they have their Beidou (Compass) GNSS system which complements GPS, GLONASS, Galileo, QZSS, etc.There are Taiwanese fabs that make GPS receiver chips.

author: JS
author_rank: Frequent Contributor
timestamp: August 21, 2018, 01:23:10 am
content: I said cheap CN, like counterfit ICs, of course there are CN production of such ICs but not redesign of fake without the locking for speed and altitude... I doubt that, not that there is fabrication of ICs in CN or even counterfits.JS