Feb 1, 2011. For a simulation of
a correct position calculations needs to develop
a software with 3 simulation satellites on different orbits with a simulation
probe calculating distances btw a probe and satellites with a random (set by some
parameters) error. Output must be in ID 28 ID 30 format (a floating point).
The output fill be stored in onboard storage. Then main onboard computer (backup
too) can have access to the data – to process and to calculate current position. For
a calculation of a such position enough to calculate Kepler’s elements of a probe’s
orbit in a moment of time in a past.
The Simulation software will be based on an existing Sun-Earth-Moon-satellite
simulation package developed for a probe’s orbit/flight-path calculation by
adding 3 more bodies (satellites) to simulate. A random error will be introduced
to estimate the time for a correct orbit’s calculation, and a possible error in
a positioning.
Formulas for calculation at :
http://ru.wikipedia.org/wiki/%D0%9E%D1%80%D0%B1%D0%B8%D1%82%D0%B0%D0%BB%D1%8C%D0%BD%D0%B0%D1%8F_%D1%81%D0%BA%D0%BE%D1%80%D0%BE%D1%81%D1%82%D1%8C
And at:
http://sat-media.net/faq/orbita.htm
Also useful formulas at:
http://ru.wikipedia.org/wiki/%D0%93%D0%B5%D0%BE%D1%81%D1%82%D0%B0%D1%86%D0%B8%D0%BE%D0%BD%D0%B0%D1%80%D0%BD%D0%B0%D1%8F_%D0%BE%D1%80%D0%B1%D0%B8%D1%82%D0%B0
Astro-orientation and gyro-orientation system design and requirements.
It is impossible to do a mission without the ability to orient probe in flight,
to calculate position, orientation, center of gravity and speed of a probe. All
this is a task for orientation system. Modern technologies allow the use of compact
gyroscopes to detect probe's X-Y-Z axes orientation, cameras to make pictures of
starts, infrared sensible sensors (cameras) to calculate celestial’s bodies horizons,
computers to make calculation and predict location of a probe.
For a prime orbit’s Keplers elements calculation considered to use GPS receiver.
It is unknown for now how GPS receiver will perform on flight with speed around
10km/s. Investigation should be done but data from experiment on satellite
position calculation was already done and published.
GPS raw data from a SiRF capable receiver with records ID 28,30 will be enough
to produce current positions of observing satellites (ID 30), and distances to
it (ID 28). Data and time for each observation will be recorder in real time.
Analyzing data with assumption that orbit is ellipsoid lay in one plane can give
data to calculate major axes and parameters for a plane. Algorithms first will
approximate plane direction (inclination, longitude of ascending node), then
major axes (eccentricity, argument of perihelion) , then point on an ellipse can
be calculated to get mean anomaly.
Kepler’s elements needs to be assumed stable (atmospheric influence will be
small and can be accounted) that limitation will give constrain on errors
sampling GPS raw data. For testing formulas and algorithms on a ground prior
launch can be assumed that initial plane is defined by
north/south/some-equatorial points, major axes not equal each other and equal
earth radius. Then algorithms should produce plane parallel equator and point
with location of a receiver, and major exes will be equal radius of calculated
plane.
Different type gyroscopes was investigated by parameters and tested. Results give requirements for gyro-platform
design, which include temperature restriction, functionality, location, precision,
data bandwidth requirements. Precision of a collected data should give requirements
for high-thrust engine and low-thrust engine. For example: delays in gyroscopes
sensor’s calculation and delays in orientation’s controls motors can create unstable
thrust’s vectors, and compensation by reducing thrust must be apply.
Performance in vacuum, in different temperature conditions, under stress of
vibration, at landing impact have to be tested. Performance of different lenses
(plastic, glass, diaphragms) for different wavelength has to be performed. Power
consumptions, assembling capabilities, supporting electronics have to investigate
and consider in requirements for probe’s imaging system. Data capabilities / compression
capabilities of supporting electronics has to give requirements for Communication
system and Data Transfer system.
Position, orientation, speed, centre of gravity of a probe will be stored in 3 separated
location. This will include computer's memory and
non voltage memory. Verification, calculation and correction of position + orientation
can be update by astro-orientation, gyro-orientation system and from mission control.
History data of position and orientation enough for on board calculation should
be stored in on board computers and can be update/corrected by mission control.
Probe’s orientation on all stages must be able to execute 4 different tasks:e 4 different tasks:
- centre of gravity positioning, for orientation at main impulses engine’s firing;
- centre of gravity positioning, for changing vector of thrust for low-thrust engine;
- probe’s rotation in axes X-Y-Z before engines firing;
- probe’s rotation in axes X-Y-Z of a probe's manipulator(s), antenna(s), tools,
engines components positioning.
All orientation commands have to be done by (a) main on board computer; (b) backup
on board computer; (c) mission control. In an absence of communication with mission
control all pre-programmed orientations targets will be executed. Mission control can specify source for control devices either
with on-board computers, or mission control itself, all settings for all control
devices must time out to execute, first-in-last-out fixed size command stack with
default (top-of-stack) command's values.
Reference for SiRF can be found at
http://gpsd.berlios.de/vendor-docs/sirf/SiRF2-Navman.pdf
Reference for ID 28 and ID 30 - see the same document.