Last week NASA announced that it had selected the HP iPAQ h5550 for use aboard its spacecraft and the International Space Station. According to a report on infoSync World, NASA chose this iPAQ because it was one of the few handhelds that could pass its flight certification tests with almost no modification.
I did some research into the iPAQ h5550 to see what its features are, and the results were pretty confusing. The h5550 has been available since mid 2003, but it's rather difficult to find from on-line merchants. infoSync World reviewed the h5550 and h5555 at the same time but focused on the h5550 and didn't really explain the relationship between the two. BargainPDA explained that the iPAQ 5550 and 5555 are "essentially the same unit" and mostly differ in terms of the software bundled with the unit for retail sale and possibly the reseller from which the PDA is purchased.
The iPAQ 5500 series have the same form factor as the original iPAQ's from Compaq. This means that they are huge: 5.43" long x 3.3" wide x 0.63" thick. The 5550 and 5555 both weigh in at 7.2 ounces. The advantage of this large size is that the display can be a bit larger than most PocketPC handhelds.
The 5550 and 5555 both have integrated WiFi (802.11b) and Bluetooth. It's not clear from my research whether the International Space Station has WiFi installed or not, but it's reasonable to conclude that it has, since this is one of the main features of the iPAQ that NASA chose.
The first iPAQs were launched into space on April 19, according to HP's press release. They are being used as "mobile productivity tools to record daily crew procedures, write personal memos and check e-mail and calendars. The space crew will also be able to listen to music, view photos from home and read e-books, allowing them to have some of the comforts of home on their journey." Apparently, two iPAQs will be kept permanently on the ISS, with two more being sent up on the next expedition.
If you are interested in getting a PocketPC that is so sturdily built that it is considered suitable for space travel by NASA's flight engineering people, I'd recommend the iPAQ h5555. It's much more widely available than the h5550, and is the same in terms of processor, OS build, display, and memory.