Hyperspectral Imaging Satellite and Water Propulsion System in CubeSats
Science & Technology › Space Technology and ISRO · Topic 12.25
A hyperspectral imaging satellite carries a sensor that records the light from each point on the ground in hundreds of narrow, adjacent wavelength bands, instead of the few broad bands of ordinary cameras. This gives a detailed spectrum for each pixel, which acts like a fingerprint that can tell apart crop types, minerals, water quality and pollution. India's first such satellite, HySIS, was launched by PSLV-C43 on 29 November 2018 along with 30 foreign satellites from eight countries. Water propulsion uses water as the propellant of a small thruster for CubeSats: electrolysis can split water into hydrogen and oxygen that are burned, or heated water makes steam, giving a safe, low cost and non-toxic way to manoeuvre small satellites.
5 min read · UPSC Prelims · Science & Technology · Space Technology and ISRO
At a Glance
- HySIS launched 29 November 2018, PSLV-C43
- Bands Hundreds of narrow bands
- Compared with Multispectral, few bands
- CubeSat propulsion Water as propellant
- Benefit Safe and low cost
- Exam link UPSC Prelims, Science & Technology: Space Technology and ISRO
Where Does It Fit?
This topic follows the account of NASA’s asteroid mission. It returns to two technologies that increase the value of small satellites, better sensors and safer, cheaper propulsion. Previous topic: NASA’s Asteroid Impact and Deflection Assessment Mission. Next topic: Cassini Mission to Saturn and OSIRIS-REx Mission to Asteroid Bennu.
What Is Hyperspectral Imaging?
| Item | Details |
|---|---|
| Multispectral | A few broad bands, for example green, red and near infrared, as on Resourcesat |
| Hyperspectral | Hundreds of bands, each only a few nanometres wide, forming a continuous spectrum for every pixel |
| HySIS | Hyperspectral Imaging Satellite of ISRO. Orbit about 636 km. Mass about 380 kg. Bands in visible and near infrared (55 bands) and shortwave infrared (about 256 bands) |
| Launch | PSLV-C43 from Sriharikota on 29 November 2018, along with 30 satellites from eight countries including the United States |
| Spatial resolution | About 30 m |
| Spectral signature | Each material reflects light differently at each wavelength, so the spectrum identifies it |
| Data cube | Hyperspectral data form a three dimensional cube of two spatial dimensions and one spectral dimension |
What Are the Uses and What Is Water Propulsion?
- Agriculture: crop type, stress, nutrient and disease detection
- Mineral exploration: identifying minerals by their absorption features
- Environment: water quality, algal bloom and oil spills
- Forestry: species mapping and forest health
- Defence: identifying camouflaged objects and materials
- Private missions: Pixxel, an Indian start-up, launched its first hyperspectral satellites in 2022 and 2024 as part of a constellation
- Water propulsion: the thruster stores water, splits it into hydrogen and oxygen by electrolysis using solar power, and burns the gases to give thrust
- Steam thruster: a simpler design heats water into steam for a low thrust jet
What Else Should You Remember?
- Why CubeSats need propulsion: to raise or lower their orbit, avoid collisions and remove themselves at the end of life
- Safe propellant: water is non-toxic, non-flammable on the ground and needs no special handling, so it can be loaded easily
- Pressure and storage: water can be stored as a liquid at low pressure, reducing risk for the main rocket that carries a CubeSat as a secondary passenger
- Example: NASA’s Pathfinder Technology Demonstrator-1 mission carried a CubeSat with a water electrolysis thruster called Hydros-C in 2022
- Performance: thrust is low, but the specific impulse is moderate, about 300 to 400 seconds
- Other CubeSat propulsion: cold gas, pulsed plasma, electrospray and ion thrusters, as in Space Technology Innovations: Nanosatellites, Electric Propulsion, Satellite-Based Internet
- Debris: propulsion allows CubeSats to deorbit, which reduces the debris problem, as in Space Junk and Graveyard Orbits
- Hyperspectral data volume: the large data volume needs onboard processing and fast downlink
- Calibration: sensors must be carefully calibrated against ground measurements
- Indian effort: ISRO has said that new hyperspectral missions are planned, and private firms are building small hyperspectral satellites, in line with the aim of a larger Earth observation constellation
- Related method: thermal infrared imaging and radar add other kinds of information, as in Remote Sensing Applications and Ground Segment Services
- Caution: specific results of individual missions should be checked from official sources before quoting
- Spectral libraries: reference spectra of minerals, crops and water types are stored in libraries, and matching them with satellite spectra identifies materials automatically
- Atmospheric correction: gases and aerosols alter the spectrum seen from space, so data are corrected before use
Why Does It Matter for the Exam?
- Difference: hyperspectral versus multispectral
- Facts: HySIS launch date and rocket
- Uses: minerals, crops, pollution
- Current affairs link: Pixxel and CubeSat propulsion
- Common errors: confusing HySIS with Cartosat or saying it has few bands
As an analytical point, hyperspectral data bring a step change in what satellites can detect. Combined with safer small satellite propulsion, they allow cheap constellations that watch the Earth often and in fine detail.
Why Is This Topic Important?
- Sensor Hundreds of bands
- HySIS India’s satellite
- Propulsion Water thruster
What Came Next?
The next topic covers the Cassini mission to Saturn and the OSIRIS-REx mission to the asteroid Bennu. Next topic: Cassini Mission to Saturn and OSIRIS-REx Mission to Asteroid Bennu.
Key People and Terms
- Hyperspectral Hundreds of narrow bands
- Spectrum Light split by wavelength
- Electrolysis Splitting water by current
- Thruster Small rocket engine
- Pixel Image element
- Data cube 3D spectral data
Exam Corner
Points to Remember
- HySIS launched: 29 November 2018 by PSLV-C43.
- Hyperspectral = hundreds of bands.
- Multispectral = few bands.
- Water thruster uses electrolysis.
- 30 foreign satellites in 8 countries on PSLV-C43.
Do Not Confuse With
- Hyperspectral and multispectral Hundreds versus a few bands
- HySIS and Cartosat Spectral detail versus fine spatial detail
- Water thruster and ion thruster Chemical gases from water versus electric ion beam
Memory Hook
Few bands is multi, hundreds is hyper; HySIS reads the spectrum, water makes the CubeSat move.
Mains Angle
Questions ask for the difference between sensors and uses. These points help.
- Sensor Spectral signature
- Uses Farm to mineral
- Small satellites Propulsion
A Question You May Face
An original practice question, not a past paper question.
“Explain hyperspectral imaging and discuss its applications in India along with the role of new propulsion technologies for small satellites.”
How to Answer
- Meaning Hundreds of bands.
- HySIS Facts.
- Uses Crops, minerals.
- Propulsion Water thruster.
GS Relevance
Frequently Asked Questions
What is hyperspectral imaging?
Hyperspectral imaging is a remote sensing technique in which a sensor records the light from each point on the ground in hundreds of narrow, continuous wavelength bands. Each pixel then has a detailed spectrum that acts as a fingerprint, so scientists can identify crops, minerals, vegetation health, water quality and pollutants more precisely than with ordinary cameras.
What is HySIS?
HySIS, the Hyperspectral Imaging Satellite, is an ISRO Earth observation satellite launched by PSLV-C43 on 29 November 2018. It carries sensors in the visible, near infrared and shortwave infrared regions with many bands, and is used for agriculture, forestry, coastal studies, mineral mapping and inland water monitoring.
How is hyperspectral different from multispectral imaging?
A multispectral sensor records a few broad bands, usually between three and ten, such as green, red and near infrared. A hyperspectral sensor records hundreds of narrow bands, so it gives a continuous spectrum for each pixel and can separate materials that look the same in ordinary or multispectral images.
How does a water propulsion system work for CubeSats?
A water thruster stores water as the propellant, uses solar power to split it into hydrogen and oxygen by electrolysis, and burns the two gases in a small chamber to produce thrust. Simpler designs heat the water to steam. Water is safe, cheap and non-toxic, so it suits small satellites that travel as secondary payloads.
Which Indian company builds hyperspectral satellites?
Pixxel, a Bengaluru start-up, builds small hyperspectral satellites and launched its first ones in 2022 and later years on commercial rockets. It plans a constellation that will image the Earth often and sell hyperspectral data for agriculture, mining, energy and environment monitoring.
PYQ Practice — Statement Analysis
1 A hyperspectral sensor records hundreds of narrow wavelength bands.
Giving a spectrum per pixel.
2 HySIS was launched by PSLV-C43 in November 2018.
Along with 30 foreign satellites.
3 A multispectral sensor has more bands than a hyperspectral sensor.
It has fewer.
4 A water thruster uses electrolysis to make hydrogen and oxygen.
Which are burned for thrust.
Past Mains Questions on This Topic
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