Helios (spacecraft)
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Mission type | Solar observation |
---|---|
Operator | |
COSPAR ID | Helios-A: 1974-097A Helios-B: 1976-003A |
SATCAT no. | Helios-A: 7567 Helios-B: 8582 |
Website | Helios-A: [1] Helios-B: [2] |
Mission duration | Helios-A: 10 years, 1 month, 2 days Helios-B: 3 years, 5 months, 2 days |
Spacecraft properties | |
Manufacturer | MBB |
Launch mass | Helios-A: 371.2 kg (818 lb) Helios-B: 374 kg (825 lb) |
Power | 270 watts (solar array) |
Start of mission | |
Launch date | Helios-A: December 10, 1974, 07:11:01 SLC-41 | UTC
Entered service | Helios-A: January 16, 1975 Helios-B: July 21, 1976 |
End of mission | |
Deactivated | Helios-A: February 18, 1985 Helios-B: December 23, 1979 |
Last contact | Helios-A: February 10, 1986 Helios-B: March 3, 1980 |
Orbital parameters | |
Reference system | Heliocentric |
Eccentricity | Helios-A: 0.5218 Helios-B: 0.5456 |
Perihelion altitude | Helios-A: 0.31 AU Helios-B: 0.29 AU |
Aphelion altitude | Helios-A: 0.99 AU Helios-B: 0.98 AU |
Inclination | Helios-A: 0.02° Helios-B: 0° |
Period | Helios-A: 190.15 days Helios-B: 185.6 days |
Epoch | Helios-A: January 15, 1975, 19:00 UTC[1] Helios-B: July 20, 1976, 20:00 UTC[2] |
Helios-A and Helios-B (after launch renamed Helios 1 and Helios 2) are a pair of
The Helios project set a maximum speed record for spacecraft of 252,792 km/h (157,078 mph; 70,220 m/s).
Construction
The Helios project was a joint venture of West Germany's space agency DLR (70 percent share) and NASA (30 percent share). As built by the main contractor, Messerschmitt-Bölkow-Blohm, they were the first space probes built outside the United States and the Soviet Union to leave Earth orbit.[citation needed]
Structure
The two Helios probes look similar. Helios-A has a mass of 370 kilograms (820 lb), and Helios-B has a mass of 376.5 kilograms (830 lb). Their scientific payloads have a mass of 73.2 kilograms (161 lb) on Helios-A and 76.5 kilograms (169 lb) on Helios-B. The central bodies are sixteen-sided prisms 1.75 metres (5 ft 9 in) in diameter and 0.55 metres (1 ft 10 in) high. Most of the equipment and instrumentation is mounted in this central body. The exceptions are the masts and antennae used during experiments and small telescopes that measure the zodiacal light and emerge from the central body. Two conical solar panels extend above and below the central body, giving the assembly the appearance of a diabolo or spool of thread.
At launch, each probe was 2.12 metres (6 ft 11 in) tall with a maximum diameter of 2.77 metres (9 ft 1 in). Once in orbit, the telecommunications antennae unfolded on top of the probes and increased the heights to 4.2 metres (14 ft). Also deployed were two rigid booms carrying sensors and magnetometers, attached on both sides of the central bodies, and two flexible antennae used for the detection of radio waves, which extended perpendicular to the axes of the spacecraft for a design length of 16 metres (52 ft) each.[4]
The spacecraft spin around their axes, which are perpendicular to the
Systems
Power
Thermal control
The biggest technical challenge was to avoid heating during orbit while close to the Sun. At 0.3 astronomical units (45,000,000 km; 28,000,000 mi) from the Sun, approximate heat flow is 11
The
Telecommunications system
The telecommunication system uses a radio transceiver, whose power could be adjusted to between 0.5 and 20 watts. Three antennas are mounted on top of each probe. A high-gain antenna (23
Altitude control
To maintain orientation during the mission, the spacecraft
On-board computer and data storage
The onboard controllers were capable of handling 256 commands. The mass memory could store 500
Mission profile
Helios-A and Helios-B were launched on December 10, 1974, and January 15, 1976, respectively. Helios-B flew 3,000,000 kilometres (1,900,000 mi) closer to the Sun than Helios-A, achieving
The Helios space probes completed their primary missions by the early 1980s, but continued to send data until 1985.
Scientific instruments and investigations
Both Helios probes had ten scientific instruments[7] and two passive science investigations using the spacecraft telecommuniction system and the spacecraft orbit.
Plasma experiment investigation
Measures the velocity and distribution of
- Electron detector
- Detector for protons and heavy particles
- An analyzer for protons and alpha particles with energies between 231 eV and 16,000 eV
Flux-gate magnetometer
The
Flux-gate magnetometer 2
Measures variations of the field strength and direction of low frequency magnetic fields in the Sol environment. Developed by the Goddard Space Flight Center of NASA; measures variations of the three-vector components of solar wind and its magnetic field with an accuracy to within 0.1 nT at about 25 nT, within 0.3 nT at about 75 nT, and within 0.9 nT at an intensity of 225 nT.[10]
Search coil magnetometer
The search coil magnetometer complements the flux-gate magnetometer by measuring the magnetic fields between 0 and 3 kHz. Also developed by the University of Braunschweig, it detects fluctuations in the magnetic field in the 5 Hz to 3000 Hz range. The spectral resolution is performed on the probe's rotation axis.[11]
Plasma wave investigation
The Plasma Wave Investigation developed by the University of Iowa uses two 15 m antennas forming an elecric dipole for the study of electrostatic and electromagnetic waves in the solar wind plasma in frequencies between 10 Hz and 3 MHz.[12][13][14]
Cosmic radiation investigation
The Cosmic Radiation Investigation developed by the
Cosmic ray instrument
The Cosmic Ray Instrument developed at the
Low energy electron and proton spectrometer
Developed by the Max Planck Institute for Aeronomy, the low energy electron and proton spectrometer uses spectrometers to measure particle characteristics (protons) with energies between 20 keV and 2 MeV and electrons and positrons with an energy between 80 keV and 1 MeV.[17]
Zodiacal light photometer
The Zodiacal light instrument includes three photometers developed by the Max Planck Institute for Astronomy to measure the intensity and polarization of the zodiac light in white light and in the 550 nm and 400 nm wavelength bands, using three telescopes whose optical axes form angles of 15, 30, and 90° to the ecliptic. From these observations, information is obtained about the spatial distribution of interplanetary dust and the size and nature of the dust particles.[18]
Micrometeoroid analyzer
The
Celestial mechanic experiment
The Celestial Mechanic Experiment developed by the University of Hamburg uses the Helios orbit specifics to clarify astronomical measurements: flattening of the Sun; verification of predicted general relativity effects; determining the mass of the planet Mercury; the Earth–Moon mass ratio; and the integrated electron density between the Helios spacecraft and the data receivig station on Earth.[21]
Coronal sounding experiment
The Coronal Sounding Experiment developed by the University of Bonn measures the rotation (Faraday effect) of the linear polarized radio beam from the spacecraft when it passes during opposition through the corona of the Sun. This rotation is a measure of the density of electrons and the intensity of the magnetic field in the traversed region.[22]
Mission specifications
Helios-A
Helios-A was launched on December 10, 1974, from
The probe was placed in a heliocentric orbit of 192 days with a perihelion of 46,500,000 km (28,900,000 mi; 0.311 AU) from the Sun. Several problems affected operations. One of the two antennas did not deploy correctly, reducing the sensitivity of the radio plasma apparatus to low-frequency waves. When the high-gain antenna was connected, the mission team realized that their emissions interfered with the analyzer particles and the radio receiver. To reduce the interference, communications were carried out using reduced power, but this required using the large diameter terrestrial receivers already in place thanks to other space missions in progress.[24]
During the first
Helios-B
Before Helios-B was launched, some modifications were made to the spacecraft based on lessons learned from the operations of Helios-A. The small engines used for attitude control were improved. Changes were made to the implementation mechanism of the flexible antenna and high gain antenna emissions. The
Tight schedule constraints pressed on the Helios-B launch in early 1976. Facilities damaged during the launch of the Viking 2 spacecraft in September 1975 had to be repaired, while the Viking landing on Mars in summer 1976 made the Deep Space Network antennas that Helios-B needed to conduct its science while at perihelion unavailable.
Helios-B was launched on January 10, 1976, using a Titan IIIE rocket. The probe was placed in an orbit with a 187-day period and a perihelion of 43,500,000 km (27,000,000 mi; 0.291 AU). The orientation of Helios-B with respect to the ecliptic was reversed 180 degrees compared to Helios-A so that the micrometeorite detectors could have 360 degree coverage. On April 17, 1976, Helios-B made its closest pass of the Sun at a record heliocentric speed of 70 kilometres per second (250,000 km/h; 160,000 mph). The maximum recorded temperature was 20 °C (36 °F) higher than measured by Helios-A.
End of operations
The primary mission of each probe spanned 18 months, but they operated much longer. On March 3, 1980, four years after its launch, the radio transceiver on Helios-B failed. On January 7, 1981, a stop command was sent to prevent possible radio interference during future missions. Helios-A continued to function normally, but with the large-diameter DSN antennae not available, data was collected by small diameter antennae at a lower rate. By its 14th orbit, Helios-A's degraded solar cells could no longer provide enough power for the simultaneous collection and transmission of data unless the probe was close to its perihelion. In 1984, the main and backup radio receivers failed, indicating that the high-gain antenna was no longer pointed towards Earth. The last telemetry data was received on February 10, 1986.[25]
Mission results
Both probes collected important data about solar wind processes and the particles that make up the interplanetary medium and
The observation of the zodiacal light established some of the properties of
Helios collected data about comets, observing the passage of
The radio and plasma wave detectors were used to detect radio explosions and shock waves associated with solar flares, usually during solar maximum. The cosmic ray detectors studied how the Sun and interplanetary medium influenced the spread of the same rays, of solar or galactic origin. The cosmic ray gradient, as a function of distance from the Sun, was measured. These observations, combined with those made by Pioneer 11 between 1977 and 1980 in a distance of 12–23 AU from the Sun produced a good model of this gradient. Some features of the inner solar corona were measured during occultations. For this purpose, either a radio signal was sent from the spacecraft to Earth or the ground station sent a signal that was returned by the probe. Changes in signal propagation resulting from the solar corona crossing provided information on density fluctuations.
As of 2020, the probes are no longer functional, but remain in orbit around the Sun.[26][27][1][28]
See also
References
- ^ a b c NASA Space Science Data Coordinated Archive. Note that there is no "Epoch end" date given, which is NASA's way of saying it is still in orbit.
- ^ National Space Science Data Center. NASA. Retrieved July 12, 2017.
- ISBN 978-3-642-22838-4
- ^ Helios. Bernd Leitenberger. Retrieved May 20, 2016.
- ^ Sandscheper, Günter (December 26, 1974). "The trip to hot space". New Scientist. 64 (929): 918.
- ^ a b "Solar System Exploration: Missions: By Target: Our Solar System: Past: Helios 2". Archived from the original on October 5, 2008. Retrieved November 1, 2009.
- ^ "Tracking and Data Systems Support for the Helios Project" (PDF). NASA Jet Propulsion Laboratory. Retrieved May 20, 2016.
- Bibcode:1975RF.....19..226S. Retrieved May 2, 2022.
- Bibcode:1976RF.....20...16G. Retrieved May 3, 2022.
- Bibcode:1975RF.....19..237S. Retrieved May 2, 2022.
- Bibcode:1975RF.....19..241D. Retrieved May 2, 2022.
- Bibcode:1975RF.....19..245G. Retrieved May 2, 2022.
- Bibcode:1975RF.....19..248K. Retrieved May 2, 2022.
- Bibcode:1975RF.....19..250W. Retrieved May 2, 2022.
- Bibcode:1975RF.....19..253K. Retrieved May 2, 2022.
- Bibcode:1975RF.....19..258T. Retrieved May 2, 2022.
- Bibcode:1976RF.....20...16G. Retrieved May 3, 2022.
- Bibcode:1975RF.....19..264L. Retrieved May 2, 2022.
- NSSDC Master Catalog. Retrieved May 20, 2016.
- Bibcode:1975RF.....19..268G. Retrieved May 2, 2022.
- Bibcode:1974hsde.rept...15K. Retrieved May 3, 2022.
- Bibcode:1974hsde.rept...12E. Retrieved May 3, 2022.
- ^ Administrator, NASA Content (April 17, 2015). "Helios-A Solar Probe At Launch Complex". NASA. Retrieved May 1, 2020.
- ^ "NASA - NSSDCA - Spacecraft - Details". nssdc.gsfc.nasa.gov. Retrieved May 1, 2020.
- ^ "Helios". www.honeysucklecreek.net. Retrieved May 1, 2020.
- ^ "Search Satellite Database: HELIOS 1". www.n2yo.com.
- ^ "Search Satellite Database: HELIOS 2". www.n2yo.com.
- ^ NASA Space Science Data Coordinated Archive.
External links
- Helios-A at NSSDC Master Catalog
- Helios-B at NSSDC Master Catalog
- Helios-A Mission Profile by NASA's Solar System Exploration
- Helios-B Mission Profile by NASA's Solar System Exploration
- Titan/Centaur D-1T TC-2, Helios-A, Flight Data Report
- Titan/Centaur D-1T TC-5, Helios-B, Flight Data Report
- Helios-A and -B by Honeysuckle Creek Tracking Station
- Helios webpage by Max-Planck-Institut für Sonnensystemforschung