FIXME: Feel free to make any additions or corrections.
The existing launch tower computer (LTC), the second major design
since the group’s founding, is due for an overhaul. It’s only been
two years since LTC II was put into service, but there have been rapid
advances in available off-the-shelf technology, and our understanding
of what we need (and don’t want) in an LTC has continued to evolve.
This document should be considered the source of authority for all
questions related to the design and implementation of the LTC III. If
the design of the LTC doesn’t conform to this document, either fix the
LTC, or update the document.
The single-board computer that comprises the core of the LTC.
- Launch Tower Computer (LTC)
The entire system, including the enclosure, the single-board
computer, the peripherals, etc.
LTC II Review
LiPo ignition battery.
Phidgets. Expensive (relatively), fiddly,
and require their own interface board. Their software stack is
thick and troublesome to install.
The shore power DC-DC converter integrated with the power board was
Lead-acid car batteries (LTC II’s main power source) are bulky and
The door covering the side bulkhead (power and arm switches) can’t
be closed when the shorting bar is in place. The bar has to be
stored elsewhere when the LTC not in use.
The PowerPole connectors on the bottom bulkhead are too deeply
recessed, located too close together, and poorly labeled.
LTC III Goals
Simplify! LTC II has too many circuit boards, too many wires, too
many everything. It’s difficult to service most of LTC II’s
components without major disassembly. Peripherals (sensors, relays,
etc.) should be contained on a single custom PCB.
Make it smaller. Reduce the size of the boards, batteries, and
potentially even the enclosure.
Replace LTC II’s plastic enclosure with a metal enclosure, for
durability and RFI protection.
Improve the enclosure-to-tower mounting apparatus;
make it fast and easy to mount (and dismount) the enclosure to the
tower (DIN rail mounting (or
Strive for field-replaceable units (FRU) whenever possible. FRUs
can be swapped out with basic tools, in a minimum amount of time.
Make it user-friendly (i.e., fool-proof). Any member of PSAS
should be able to achieve a high-level understanding of the LTC in a
short amount of time. Any member should be able to operate, and if
necessary service, the LTC given suitable documentation.
Conduct a thermal analysis. Do we need an active cooling system to
deal with the heat of a desert launch site?
All the ways the LTC can get the juice it needs.
The power rails the LTC provides to its various peripherals.
5 VDC rail to power to computer, etc.
12 VDC rail to ignition battery charger.
24 VDC rail to shore power.
Several external expansion power connectors; switchable by the
Stand-alone voltmeters on the front panel, for each power rail.
(Stand-alone meters have no dependency on the computer being
Front panel LEDs indicating the status of each relay, and the
Main power switch
Ignition arming switch.
Ignition shorting bar.
Label all the things! Components, connectors, switches, oh my!
Rocket umbilical. Connection state should be detectable by the
Distinct, keyed connectors for each external connection. There
should be no way to accidentally connect a data cable to a power
outlet; or to reverse the polarity of a connector.
Several Ethernet connectors that provide external access to the
LTC’s internal subnet, for debug and expansion purposes.
Several expansion trigger switches, for computer control of cameras,
etc. Switches short two external inputs together. Nate proposes
1/8" phono connectors for these.
Expansion Ethernet and power connectors can be paired up for use
with passive PoE injectors, providing single-cable power and network
support for off-board devices (e.g., weather station).
TODO: More words, please.