The evolution and design of a Space Data Acquisition (DAQ) System
A little background and history
In 1970, NASA created a Space Vehicle Design Criteria document entitled “Flight Separation Mechanisms”. A key statement in this document is as follows:
Parts of a space vehicle must be separated during flight to jettison stages and components that are no longer needed, to uncover equipment, or to deploy payloads. For a mission to be successful, the separations must occur at the correct times of flight and with minimum changes in the attitude and rotational rates (i.e., tip-off errors) of the continuing body. There must be no recontact between the separating bodies, no detrimental shock loads induced in the structure , and no excessive or harmful debris. A separation mechanism that does not meet these requirements can produce attitude errors and tumble rates of the continuing body that are too large for its attitude-control system to accommodate, can damage its structure and critical equipment, and can cause failure or degradation of the mission.
Failure of separation mechanisms has adversely affected mission performance in several instances; for example:
- A Vanguard satellite failed to achieve orbit because the second stage of the launch vehicle was damaged at separation.
- On several early satellite launches, booster stages failed to separate.
- On a military mission, the final booster stage overtook and bumped the spacecraft after separation, damaging critical equipment in the spacecraft.
- On a recent military mission, an extendible boom was damaged at separation and failed to extend.
- During an Apollo launch, the pyrotechnic shock of a separation was of sufficient magnitude to close propellant-isolation valves in the reaction-control system of the spacecraft. The crew was unable to maneuver the spacecraft until the valves could be opened.
Nuvation designed and built a data acquisition system for Space Systems Loral (SSL). The system was used to measure the shock and vibrations that occur when a spacecraft separates on its way into space. They designed the engineering prototype, which included everything from system architecture, hardware design, board-level design, FPGA design and software design. Once the prototype was complete, they worked with their mechanical engineering partner to develop a space-rated box to house the system.
In serial staging, there is a small, second stage rocket that is placed on top of a larger first stage rocket. The first stage is ignited at launch and burns through the powered ascent until its propellants are exhausted. The first stage engine is then extinguished, the second stage separates via a pyrotechnics explosion from the first stage, and the second stage engine is ignited. The payload is carried atop the second stage into orbit. Serial staging was used on the Saturn V moon rockets. The Saturn V was a three-stage rocket, which performed two staging maneuvers on its way to earth orbit. The discarded stages of the Saturn V were never retrieved.
In parallel staging, several small first stages are strapped onto to a central sustainer rocket. At launch, all of the engines are ignited. When the propellants in the strap-ons are extinguished, the strap-on rockets are discarded via pyrotechnic explosions. The sustainer engine continues burning and the payload is carried atop the sustainer rocket into orbit. Parallel staging was used on the Space Shuttle.
Some launchers, such as the Titan III's and Delta II's, used both serial and parallel staging. The Titan III had a liquid-powered, two-stage Titan II for a sustainer and two solid rocket strap-ons at launch. After the solids are discarded, the sustainer engine of the Titan II burns until its fuel is exhausted. Then the second stage of the Titan II is burned, carrying the payload to orbit. The Titan III is another example of a three-stage rocket.
Why the need for a data acquisition system?
The pyrotechnic explosions used to separate the rocket propellant systems when they are expended, have never been measures, so NASA wanted to build a system that could measure these explosions.
The design uses mainly Commercial-Off-The-Shelf (COTS) components, specifically selected for their radiation tolerant attributes. In addition to the design of the product, Nuvation developed and was responsible for the full IPC Class-3 manufacturing process, including: PCB assembly, AOI, X-ray, flying probe testing, epoxy staking, conformal coating, chassis assembly to controlled torques, chassis staking, many rounds of functional testing, and 40-hour HASS test.
- 24 independent channels of 16-bit, 150ksps Analog-to-Digital conversion
- Programmable 0-20mA current sources on all channels
- Programmable AC, DC, GND, or calibration-signal coupling on all channels
- Programmable gain amplifiers on all channels
- Programmable analog bandwidth limiting 100Hz – 27kHz, using 8th order filters on all channels
- Cutting-edge MRAM (Magnetoresistive Memory) and PRAM (Phase-Change Memory) for radiation tolerance
- Data-redundancy techniques to protect critical information
- Flash-based Microsemi FPGA with ARM Cortex soft-core processor
- ARM Firmware written in C++
- 20-Layer IPC/J-STD-001 Class 3 PCB Design
- Spacecraft data bus interface
- Radiation-hardened “kill switch” circuit
- Extensive self-diagnostic features and BIST routines
The data acquisition system, a turn-key design, is located in the center, inside of the spacecraft close to the position where the external solar panels are located just outside the vehicle.
The system takes inputs from sensors around the spacecraft, process that data and send the information back to Mission Control on Earth to analyze and study.
Their engineering prototype took approximately one year. This included designing the architecture, hardware, board level, FPGA, as well as the software.
A space-rated enclosure had to be designed and built with a Nuvation partner.
The electronics needed to be cooled, but there is no air or atmosphere in the cold void of space, therefore a fan would be useless, so this was a challenge. Conduction cooling was the best solution in which the PC board and chassis design enabled the heat to be conducted away from the electronics.
Kudos to the talented design team at Nuvation for such an innovative and reliable design.