1. Pioneer Venus: Mission Characterization
Dr. Andrew Ketsdever

2. Background
Pioneer Venus evolved from recommendations from the Space Science Board of the National Academy of Sciences
“Need” for relatively low-cost orbiters and landers to explore the planet Venus
Earth’s closest neighbor, yet relatively little was known (especially about the lower atmosphere)
What was known raised many scientific questions

3. Background What was known Questions
Planet is covered with clouds
Atmosphere primarily CO2 (Traces of sulphuric acid)
Surface pressure is 95 Earth atmospheres
Surface temperature is 493 ºC
Questions
“Why do two planets with about the same mass, probably formed out of similar materials and situated at comparable distances from the sun, have atmospheres that evolved so differently?”
“Why is the surface of Venus baked by a searing heat, while Earth is not?”
Answers to these questions should enhance knowledge of Earth’s atmosphere and weather
Venus represents a relatively simple weather “machine” absent of the influence of oceans

4. Subject: Venus Diameter: 12,100 km ( 12,745km) Mass: 0.81 M 
Density: g/cm3 ( 5.5 g/cm3)
Mean Orbital Radius: Million km
Orbital Period: days
Rotation: Once per days
Clouds rotate in about 4 days (at the top)
Rotation is retrograde
Opposite to direction that planet travels around sun
One day is 117 Earth days
Only 6º tilt of axis with respect to its orbital plane
Minimum energy launch opportunities come every 584 days

5. Subject: Venus Surface Pressure Surface Temperature Albedo
95  Atm
9,616 kPa
Surface Temperature
750 K
480 ºC
Albedo
1.82 
Nearly 1.98  solar intensity
Similar atmospheric absorption of solar energy

6. Mission Objectives
Subject: Characterization of the atmosphere, ionosphere, and surface of Venus
Objectives
Determine the composition of the clouds
Determine the composition and structure of the atmosphere from the surface to high altitude
Determine the composition and structure of the ionosphere
Determine the characteristics of the surface on a planetary scale
Investigate the interactions of the magnetic field and the solar wind
Investigate the planet’s gravitational field harmonics

7. Mission Concept Two spacecraft Orbiter Multi-probe
Spacecraft subsystems
12 scientific instruments (payloads)
Multi-probe
Spacecraft bus
3 small probes
1 large probes
DRIVER: Determine the composition and structure of the atmosphere from the surface to high altitude

8. Mission Details Pioneer Venus 1 (Orbiter)
Launched 20 May 1978
Atlas SLV-3D/Centaur
Planet Arrival 4 Dec 1978
Pioneer Venus 2 (Multi-Probe)
Launched 8 Aug 1978
Planet Arrival 9 Dec 1978 (Probes)

9. PV1: Orbit Details Type II Interplanetary Trajectory Venus Orbit
Travels more than 180º around the sun
Used to reduce the spacecraft’s velocity upon arrival at Venus
Less propellant required (180kg propellant used – 545 kg total spacecraft mass)
Travel of 480 million km, in 7 months
Venus Orbit
28 sec burn of solid propellant motor
Elliptical (300 km periapsis / 66,000 km apoapsis)
24 hr period
75º inclination
Later: Periapsis commanded to 150 km

10. PV1: Interplanetary Orbit

11. PV1: Venus Orbit

12. PV1: Venus Orbit

13. PV1: Orbit Details

14. PV2: Orbit Details Type I Interplanetary Trajectory
Travels less than 180º around the sun
Launched a few days after PV1 crossed back inside Earth’s orbit
4 month trip time
Arrival speed at Venus 19,500 km/hr (5.4 km/s)
24 days to Venus: Large probe released
20 days to Venus: Small probes released
Bus re-entry in Venus atmosphere

15. PV2: Interplanetary Orbit

16. PV2: Orbit Details

17. PV2: Orbit Details

18. The Spacecraft Built by Hughes “Aircraft” Company
Project was managed by NASA Ames RC
Expertise
High velocity (hypersonic) flight dynamics
Re-entry
Planetary atmosphere sensing (Earth demonstrations)
We will look at some of the design specifics
Orbiter (PV1)
Accomplish retro-fire at Venus to achieve specified orbit
Accommodate 47.6 kg of scientific payloads
Support dual frequency (S and X bands) for occultation exp
Multiprobe (PV2)
Mechanically and electrically support probes (1 large / 3 small)
Target and release probes at Venus
Accommodate 57.6 kg of scientific payloads

19. The Orbiter (PV1) Requirements Return data for 243 days in Venus orbit
Spin stabilization
Disk shape
Mass concentrated at perimeter (Iz/Ip = 1.2)
Solar thermal environment of up to 2 
Instrument pointing requirements ~0.2º accuracy
Atlas / Centaur upper stage
Limited mass (587.4 kg completion / 523 kg inception)
15g max vibration load
Fundamental frequency >4Hz
Shroud constrained dimensions
Clamping arrangement (LV interface)

20. The Orbiter (PV1) Spacecraft element Spacecraft bus (subsystems)
Six basic assemblies
Despun antenna assembly
Bearing and power transfer assembly (slip ring) and support structure
Equipment shelf
Solar panel
Orbit insertion motor
Thrust tube
12 scientific instruments
Mounted on periphery of equipment shelf to provide adequate viewing angles
Many instruments required diamond and sapphire windows
Isolated from spacecraft contaminants
For example, magnetometer is mounted at the end of a 15.7 ft. boom to isolate it from the spacecraft

21. Orbiter (PV1)

22. Orbiter

23. Orbiter Spin-stabilized platform Flat Cylinder Despun antenna
2.5 m diameter
1.2 m high
Despun antenna
1.09 m diameter
High gain, parabolic
S and X band operation

24. Payloads 12 scientific instruments Cloud Photopolarimeter (OCPP)
Measure vertical distribution of cloud and haze particles
5 kg, 5.4W
3.7 cm aperture telescope with filter wheel
Surface Radar Mapper (ORAD)
Produce first maps of large areas of Venus not observable from Earth
9.7 kg, 18W
150 m resolution
Infrared Radiometer (OIR)
Measure infrared radiation emitted by the atmosphere at various altitudes
5.9 kg, 5.2W
Determine where maximum deposition from solar energy is located

25. Payloads Airglow Ultraviolet Spectrometer (OUVS)
Measure UV light scattered or emitted by clouds
3.1 kg, 1.7W
Airglow is the absorption of UV light by gases in the upper atmosphere
Neutral Mass Spectrometer (ONMS)
Measure neutral atom and molecular densities
3.8 kg, 12W
Vertical and horizontal distribution of neutral gases
Solar Wind Plasma Analyzer (OPA)
Measure properties of the solar wind at Venus (density, velocity, flow direction, temperature)
3.9 kg, 5W
Electrostatic energy analyzer
Magnetometer
Investigate weak magnetic field of Venus
2 kg, 2.2W
Weak magnetic field may play an important role in solar wind interactions

26. Payloads Electric Field Detector (OEFD)
Measure electric fields of plasma waves and radio
emissions from 50-50,000Hz
0.8 kg, 0.7W
Answer questions about how the solar wind is deflected
around Venus
Electron Temperature Probe (OETP)
Measure thermal characteristics of ionosphere
2.2 kg, 4.8W
Electron temperature, density and spacecraft potential
Ion Mass Spectrometer (OIMS)
Measure distribution of charged particles in the atmosphere
3 kg, 1.5W
Positive charge distribution and concentrations
Charged-Particle Retarding Potential Analyzer (ORPA)
Measures the energy of ions in the ionosphere
2.8 kg, 2.4W
Velocity, temperature and concentration of most abundant ion species
Gamma Ray Burst Detector (OGBD)
Measure gamma ray bursts from outside the solar system
2.8 kg, 1.3W
Gamma ray energies from 0.2 to 2 MeV
Radio Science Experiments
Occultation of X and S bands (atmosphere)
Doppler shifts (spacecraft accelerations)

27. Spacecraft Configuration

28. Attitude Determination and Control
Shape and weight distribution conform to basic mechanical requirements for a spin stabilized vehicle
Roll-to-Pitch Ratio greater than one
Attitude determination
Dual slit sun sensor (x3)
Star sensor
Propulsion provided control
Spin rate
Attitude control
Orbit insertion

29. Attitude Control Thrusters

30. Propulsion Attitude control 7 total thrusters
Liquid monopropellant hydrazine (N2H4)
23.78 kg of propellant required (spin, despin, orientation)
Catalytic decomposition
4.45 N of thrust (each)
Blow-down mode
System
Tanks and Pressurant (He)
Resevoir (60 sec of propellant – 5 sec of spin up thrust required)
Filters
Feedlines
Heaters (to prevent freezing)
Valves
Thrust chamber
Nozzle

31. Propulsion

32. Propulsion Orbit insertion 1 thruster System Solid propellant
18000 N of thrust provided
ΔV ~ 1.05 km/sec
System
Tank
Insulation
Safe and arm unit (igniter)
Nozzle

33. The Multiprobe (PV2) Requirements
Same basic structure as PV1 (for bus)
Bus spin stabilization
Disk shape
House 1 large and 3 small probes near cg plane
Probes to inner atmosphere and surface
Not required to survive impact with surface
Solar thermal environment of up to 2 
Bus pointing accuracy for probes and instruments
Atlas / Centaur upper stage
Limited mass (905.4 kg completion / kg inception)
15g max vibration load
Fundamental frequency >4Hz
Shroud constrained dimensions
Clamping arrangement (LV interface)

34. The Multiprobe (PV2) Spacecraft element Spacecraft bus Large probe
Similar in design to Orbiter
2 scientific instruments
Five basic assemblies
Large probe support
Small probe support
Equipment shelf
Solar Panel
Thrust tube
Large probe
Released from bus
Seven scientific instruments
Three small probes
Released from bus after large probe
Three scientific instruments

35. Multiprobe (PV2)

36. Large Probe (Payload)
The Pioneer Venus large probe was equipped with 7 science experiments, contained within a sealed spherical pressure vessel.
After deceleration from initial atmospheric entry at about 11.5 km/s near the equator on the Venus night side, a parachute was deployed at 47 km altitude.
The large probe was about 1.5 m in diameter and the pressure vessel itself was 73.2 cm in diameter. Pressure vessel was Titanium filled with 102 kPa of Nitrogen.
Weight: 315 kg
The science experiments were:
a neutral mass spectrometer to measure the atmospheric composition
a gas chromatograph to measure the atmospheric composition
a solar flux radiometer to measure solar flux penetration in the atmosphere
an infrared radiometer to measure distribution of infrared radiation
a cloud particle size spectrometer to measure particle size and shape
a nephelometer to search for cloud particles
temperature, pressure, and acceleration sensors

37. Large Probe 1 – Radio Transparent Window 2 – Aft Cover 3 – Antenna
4 – Pressure Vessel
4.1 – Parachute Tower
5 – Cloud Particle Spectrometer
5.1 – Neutral Mass Spectrometer
5.2 – Solar Flux Radiometer
6 – Deceleration Module
4.1
5.2
5.1

38. Large Probe

39. Small Probes The three small probes were identical
0.8 m in diameter, 90 kg
Spherical pressure vessels filled with
102 kPa of Xenon
Unlike the large probe, they had no parachutes
Aeroshells did not separate from the probe
Instruments
Nephelometer and temperature, pressure and acceleration sensors, as well as a net flux radiometer experiment to map the distribution of sources and sinks of radiative energy in the atmosphere
The radio signals from all four probes were also used to characterize the winds, turbulence, and propagation in the atmosphere.
The small probes were each targeted at different parts of the planet and were named accordingly.
The North probe entered the atmosphere at about 60 degrees north latitude on the day side.
The night probe entered on the night side.
The day probe entered well into the day side, and was the only one of the four probes which continued to send radio signals back after impact, for over an hour.

40. Small Probe 1 – Antenna Housing 2 – Temperature and Pressure Sensors
3 – Deceleration Module (carbon phenolic heat shield)
4 – Hermetically Sealed Container
5 – Nephelometer
6 – Net Flux Radiometer

41. Probes

42. Propulsion Attitude control No orbit insertion motor required
Same as for Orbiter with one less thruster
6 total thrusters
Liquid monopropellant hydrazine (N2H4)
15.34 kg of propellant required (ΔV, spin, despin, orientation)
Catalytic decomposition
4.45 N of thrust (each)
Blow-down mode
No orbit insertion motor required

43. REFERENCES
Fimmel, R., Colin, L., Burgess, E., Pioneer Venus, NASA SP-461, 1983.
Brodsky, R., Pioneer Venus: Case Study in Spacecraft Design, AIAA, 1980.
“Pioneer Venus”, Press Kit, Release 78-68, NASA, 1978.
Venus and Mars: Atmospheres, Ionospheres and Solar Wind Interactions. (edited by J.G. Luhmann, M. Tatrallyay and R.O. Pepin) , American Geophysical Union, 1992.