Tim, Glenn and Andrew had a conference call with Glen Gardner, who has designed several experiments for NASA sounding rockets. Information on Glenn can be found at http://members.verizon.net/~vze24qhw. David Hunter knows Glen, so thanks to Dave for roping him into a conference call with us.
Point number one: We may be idiots, but we're not dumb idiots. It turns out that a lot of the practices of the NASA sounding rocket folks is pretty similar to us, or at least we're vaguely aware of the relevant issues.
Here's an experiment that Glen worked on:
Here's some notes from the conversation with Glenn:
- They used 1/4 in thick gray plastic dielectric CPA with copper on the back and a circuit board on the front, just like us.
- Glen thinks that they used cicurlarly polarized patches instead of a single linear patch like us.
- Doesn't know what the dielectric is; it's not epoxy. Teflon? Polytehelene? Looks like it was poured in place... a polyeurthane foam?
- The copper clad they used was G10 - the non fire retardent board, unlike FR4 (http://www.eagleware.com/pdf/apps/2015_DesigningVCOonFR4.pdf)
- Bristol aerspace made the antenna
- Spherical propagation pattern
- They used 10W and 4W transmitters - he says "as much power as possible"
- Split ring, just like us. SMA on the back.
- Their telemetry was 4Mbps! Working on upping it to 8Mbps
- They used a coating of gray RTV sprayed on the rocket to deal with the heat... it ablated away but kept the Al nosecone cool
Batteries and power
- Used solder-tabbed NiCds - proven technology, rechareable with shore power.
- +/- 18 V pack
- DSP 14W, all like 50W
- Used one pack for develeopment, another for flight
Black Brant stuff
- 300 lbs of lead weight to get the trajectory they wanted!
- 18" diameter
- Like 1100 lb avionics + airframe + payload (not including motor)
- No guidance, but there was attitude control: Space Vector
- In New Mexico they use small canard wings for guidance so they don't hit CA.
- Scrounged used military gyros for attitude
- 8 - 12g ride... everything build for 25g's and tested at 20g's
- Mostly doesn't use microcontrollers
- Mechanical timers and switches for flight sequencing
- Actel microcontrollers?
- Uses 50 pin D connector as umbilical
- Anything that shakes becomes a hammer; dampen resonances
- They dampened everything (like wires) with RTV
- No zip ties, they work loose
- They lace everything with teflon laces (not wax - they outgass)
- No lock washers - they use red (permanent) and blue (removable) lock tight together to make "purple" locktight... but this basically makes the screw a one shot deal if you have to unscrew it.
- Screw heads can snap off, so coat the screw heads with RTV so they're at least removed.
- "Stake" everything - attach it everywhere
- Conformal coat the boards for metal flying about... happens a lot
- Extra holes in the boards for stiffening
- Surface mount components must be examined with a microscope.
- 19-21 wire Teflon wire.. not the usual 7 wire.
- Make their own bundles.
- They use gold plated milspec D connectors.
- They don't like SMA's or BNC's - they use SMB's with RTV to hold together
- Last minute reconfigurations on the rail - "rocket tape" (green ducttape)
- Use MDM connectors - a small D sub (via Newark or Glenair) with wires pre-installed.
- Latch ups in microcontroller - requires external _power cycling watchdogs to unlatch it (within milliseconds)
- Did a 700km flight with a PIC16F84 and no watchdog.
- Always use connectors going into a box
- Uses Bardington magnetometers for nav
- Uses brass, Ti, nonmagnetic stainless, teflon coax can have a steel center conductor - non-magnetic stainless from McMaster Carr
- Crystals go nuts on launch - they use crystal-based clock oscillators (tin cans) for a reliable, spec'd clock
- On launch, everything goes nuts and drops in and out.. need to come up from reset correctly.
- Maybe use an supercap for small dropouts.
- Write code in statemachine for so that on reset you can get back to where you were.