Robot
Probes |
What instruments would you place on a robot space probe?
The Viking space probes (Viking 1 and Viking 2) were two NASA
missions to explore Mars in the 1970s. Both missions deployed a
pair of robot probes: one lander and one orbiter. These probes
were very advanced at the time and are still technological marvels
today: they are fine examples of human ingenuity. The diagram
above shows a Viking lander (landing probe) and a labeled version
is given below.
Viking Lander
Technical Specifications
Length: 3m; Height: 2m
Mass (fully fitted): 576 kg
The body platform of each lander is hexagonal and constructed from
aluminium and titanium alloys. Three alternate sides are shorter, such
that in plan view the body resembles a triangle with blunted corners
with a landing leg on each short side. The body is covered in spun
fiberglass and Dacron cloth to protect equipment and conserve heat. the
lander and external assemblies are painted light grey (with a
rubber-based silicone)to protect it against abrasion and reflect solar
heat.
Deployment of the
Landing Probes
Viking 1 landed on Mars in the Chryse Planitia (Plane of Gold, 22.697 oN)
in July 1976.
Viking 2 landed on Mars in the colder Utopia Planitia (Plane of
Paradise, 48.269 oN) in September 1976.
The lander (landing probe) and aeroshell separate from
the orbiter (orbiting probe), placed in orbit around Mars, and
descend. The aeroshell acts as a heat shield and carried out some
measurements on the upper atmosphere (composition and ionization). It
also possessed 12 hydrazine mono-propellent thrusters to maneuver the
lander and direct it to the chosen landing site. The lander and
aeroshell were encased in two bioshield valves, which enclosed
them like an egg. These ensured that the lander remained sterile during
launch and were jettisoned on leaving Earth orbit. Prior to launch, the
entire assembly inside the bioshield was sterilised by heating to high
temperatures to prevent accidental contamination of Mars by
microorganisms from Earth.
the lander was initially connected to the orbiter by an umbiliocal
cord during the cruise phase to Mars, which allowed power and data
transmission. An additional base cover over the top of the
lander (between the lander and the bioshield cap) protected the lander
during initial entry. The parachute system and the mortar to
fire the chute were situated on top of the lander beneath the base
cover.
The descent capsule (consisting of lander, aeroshell and base
cover) separated from the orbiter and first traversed the interplanetary
medium permeated by the solar wind. The following details the descent of
Viking 1. The capsule entered the upper atmosphere of Mars at 250 km
altitude at about 1600 km/h, with the aeroshell heat shield directed
forwards. Friction between the atmosphere and aeroshell slowed descent
and caused temperatures to reach something like 1500 C. The heat shield
had a sacrificial outer surface layer which burnt away, as intended,
carrying away much of the heat with it. The aeroshell provided some
aerodynamic lift at about 30 km. At 6.4 km and 1600 km/h the parachute
was deployed and seven seconds later the aeroshell was ejected and the
lander's three legs extended. After about a minute the chute had slowed
the lander to 60 m/s. At 1200 m the lander's three terminal descent
engines ignited and the chute and base cover were jettisoned.
Orbiting Probe
Specifications
The orbiter (2 325 kg, 3.3 m in height) was equipped with a visual
imaging subsystem (VIS), an infrared thermal mapper (IRTM)
and the Mars atmospheric water detector (MAWD). The VIS
consisted of a pair of identical cameras and telescopes and was used in
imaging and selecting suitable landing sites for the landing probes and
to map the planet's surface globally. The IRTM mapped temperatures on
the planet's surface, which provided data on surface composition and
roughness and internal heat sources, e.g. due to underlying magma
pockets. The MAWD was an infrared spectrometer used to map the
distribution of water vapour over the planet's surface, providing data
on weather and seasons. The orbiter was powered by four solar panels
(total surface area 15 m2 and a total span of 9.7 m) and
equipped with nitrogen gas thrusters. A Sun sensor maintained lock on
the Sun for navigation and orientation (the Sun provided a reference for
pitch and yaw). The star Canopus, monitored by the Canopus sensor, was
also used as a fixed reference point for roll). The brain of the orbiter
consisted of two onboard computers with 4096 (computer) words of
plated-wire memory. A moveable 1.5 m dish antenna provided remote
high-gain S-band communication with Earth (that is by means of a
directed radio beam) while an additional low-gain antenna (operating in
all directions) provided communications when nearer to Earth. (S-band is
a specified range of microwave frequencies).
Landing Probe
Specifications
Did you think to include all these things on your robot probe?