UPSC Prelims 2020 Q43: Science & Technology – Space Technology & Astronomy
- (a) Voyager - 2
- (b) New Horizons
- (c) LISA Pathfinder
- (d) Evolved LISA
Answer: (d) Evolved LISA
Explanation
Space Experiment: Spacecraft Formation
| Mission | Spacecraft formation/purpose? |
|---|---|
| Voyager-2 | Single spacecraft; interplanetary probe |
| New Horizons | Single spacecraft; Pluto/KBO reconnaissance |
| LISA Pathfinder | Single spacecraft; test for LISA |
| Evolved LISA | Three spacecraft in formation; gravitational waves |
Evolved LISA (Laser Interferometer Space Antenna): Proposed ESA/NASA mission to detect gravitational waves. Three spacecraft in equilateral triangle formation (sides ~1 million km) with lasers measuring distance between them.
When gravitational waves pass, they distort spacetime, changing distances between spacecraft. LISA Pathfinder (2015-2019) was a single-spacecraft test; full Evolved LISA will have three craft.
Answer: (d) Evolved LISA.
Why each option is right or wrong
- (a) Incorrect. Voyager-2 is single spacecraft, not triangular formation.
- (b) Incorrect. New Horizons is single spacecraft.
- (c) Incorrect. LISA Pathfinder was single craft (test for future Evolved LISA).
- (d) CORRECT. Evolved LISA uses three spacecraft in equilateral triangle (1 million km sides) with lasers measuring distortions from gravitational waves.
Key point
Evolved LISA: ESA/NASA gravitational wave detector. Three spacecraft ~1 million km apart. Laser interferometry measures spacetime distortions from merging black holes, neutron stars. Scheduled launch ~2030s.
Remember
The experiment described - three spacecraft flying in equilateral triangle formation (sides one million kilometers) with lasers measuring distances - refers to the Evolved LISA (Laser Interferometer Space Antenna), a proposed ESA/NASA mission to detect gravitational waves in space.
Common mistakes
- Confusing LISA Pathfinder (single test craft, 2015-19) with Evolved LISA (three-craft formation).
- Assuming gravitational wave detection only possible from ground (LIGO). Space-based LISA detects lower frequencies missed by LIGO.
- Missing the 1 million km scale - vastly larger than LIGO (4km arm), allows detection of supermassive black hole mergers.
Exam tip
Gravitational wave detection: Ground-based LIGO (detected 2015, Nobeled 2017) detects high-frequency waves (stellar-mass BH mergers). Space-based LISA detects low-frequency waves (supermassive BH mergers, primordial waves).
Sources
- ESA - Evolved Liszt Mission Proposal
- LISA Collaboration - Science Case for LISA