BPSC 70th CCE Re-exam Prelims General Studies · Question 111 of 142

Correct — A, 7. Aditya-L1, India's first dedicated solar observatory, carries seven scientific payloads, and they divide four to three. The four remote-sensing instruments look at the Sun: the Visible Emission Line Coronagraph (VELC), the primary payload, built by the Indian Institute of Astrophysics, Bengaluru, which images and takes spectra of the corona; the Solar Ultraviolet Imaging Telescope (SUIT) from the Inter-University Centre for Astronomy and Astrophysics, Pune, which images the photosphere and chromosphere in the 200 to 400 nanometre band; and two X-ray spectrometers from the U. R. Rao Satellite Centre, the Solar Low Energy X-ray Spectrometer (SoLEXS) for soft X-rays and the High Energy L1 Orbiting X-ray Spectrometer (HEL1OS) for hard X-rays, both observing the Sun as a star. The three in-situ instruments sample the space around the spacecraft: the Aditya Solar wind Particle Experiment (ASPEX) from the Physical Research Laboratory, Ahmedabad, for protons and heavier ions; the Plasma Analyser Package for Aditya (PAPA) from the Space Physics Laboratory at VSSC for electrons and heavier ions; and a pair of Advanced Tri-axial High Resolution Digital Magnetometers on a deployable boom, which measure the interplanetary magnetic field. The 1,500 kg spacecraft was launched on PSLV-C57 on 2 September 2023 from the Satish Dhawan Space Centre and was inserted into a halo orbit around the Sun–Earth Lagrange point L1, about 1.5 million km from Earth, on 6 January 2024 — 126 days after launch.

• (b)5 — Too few, and a plausible guess for anyone who remembers only the headline instruments — the coronagraph, the ultraviolet telescope and the two X-ray spectrometers — and forgets that the in-situ package is counted as three separate payloads, including the magnetometers.
• (c)6 — One short, which is exactly what happens if the tri-axial digital magnetometers are treated as instrument hardware rather than as a payload in their own right. ISRO's own payload table lists them as the seventh payload, developed by the Laboratory for Electro Optics Systems, Bengaluru.
• (d)9 — Too many, and the option is there for the candidate who counts sub-sensors instead of payloads: ASPEX and PAPA each contain two separate spectrometer or probe units, so an instrument-by-instrument count inflates the total. The figure ISRO publishes, and the one the question wants, is seven payloads.

A Lagrange point is a position in the Sun–Earth system where the gravitational pull of the two bodies and the orbital motion of a spacecraft balance, so that the spacecraft keeps station with the Earth as both go round the Sun. L1 lies between the Earth and the Sun at about 1.5 million km — roughly one hundredth of the Earth–Sun distance — and it is the natural post for a solar observatory, because a satellite there has an uninterrupted view of the Sun with no eclipses or occultations by the Earth. Aditya-L1's science divides along the same line as its instruments. The remote-sensing payloads attack the classic unsolved problems of solar physics: why the corona is millions of degrees hotter than the visible surface below it, and how flares and coronal mass ejections begin. The in-situ payloads measure what actually arrives at L1 — the solar wind's particles and the interplanetary magnetic field — which is the raw material of space-weather forecasting, since a disturbance detected at L1 reaches the Earth some tens of minutes later.

Mission questions in state exams are answered from a fixed set of five numbers, so build them for every major mission: the launch date, the launch vehicle, the destination or orbit, the mass, and the number of instruments. For Aditya-L1 that is 2 September 2023, PSLV-C57, a halo orbit at L1, 1,500 kg and seven payloads. The reason the payload count is asked at all is that it is unusually clean — ISRO's own material states four remote-sensing and three in-situ payloads, and four plus three is a structure that is easier to hold than a bare number. Be careful about two ways of miscounting: several payloads contain more than one sensor, and the magnetometer pair on the boom is a single payload despite being two sensors. Note also the neighbouring mission that shares the year and is often confused with it — Chandrayaan-3, which landed on 23 August 2023, ten days before this launch, and which is a lunar mission with a different instrument set entirely.

• Aditya-L1 carries seven payloads — four remote-sensing (VELC, SUIT, SoLEXS, HEL1OS) and three in-situ (ASPEX, PAPA and the Advanced Tri-axial High Resolution Digital Magnetometers)
• It was launched on PSLV-C57 at 11:50 IST on 2 September 2023 from the Satish Dhawan Space Centre, Sriharikota; the spacecraft mass is about 1,500 kg
• It was inserted into a halo orbit around the Sun–Earth Lagrange point L1 on 6 January 2024, 126 days after launch; L1 lies about 1.5 million km from Earth and the halo orbit has a period of roughly 178 days
• VELC, the primary payload, was built by the Indian Institute of Astrophysics, Bengaluru; SUIT by IUCAA, Pune; SoLEXS and HEL1OS by the U. R. Rao Satellite Centre; ASPEX by the Physical Research Laboratory, Ahmedabad; PAPA by the Space Physics Laboratory, VSSC
• L1 gives a continuous, unobstructed view of the Sun with no eclipses, which is why it is the standard station for solar and space-weather observatories

• Counting sensors instead of payloads — ASPEX and PAPA each contain two sensor units, and the magnetometers are two sensors forming one payload
• Placing Aditya-L1 in orbit around the Sun or on a flight to the Sun; it orbits a point, in a halo orbit around L1, and stays about 1.5 million km from Earth
• Confusing the dates of the two 2023 missions — Chandrayaan-3 landed on 23 August 2023, Aditya-L1 launched on 2 September 2023

BPSC asks the countable fact — how many payloads, which launch vehicle, which date — so a mission has to be revised as a short table of numbers. UPSC asks what the mission is for and what the science means: what a solar storm would do to the Earth, what a mission achieved and in which attempt. Prepare the numbers for the state paper and the purpose for the central one.

• practice — not a real PYQ

  Aditya-L1 has been placed in a halo orbit around which point ?

  • (a)The Sun–Earth Lagrange point L1
  • (b)The Sun–Earth Lagrange point L2
  • (c)The Earth–Moon Lagrange point L1
  • (d)A geostationary point above the equator

  Answer(a) The Sun–Earth Lagrange point L1 — about 1.5 million km from Earth towards the Sun, giving a continuous view of the Sun without eclipses.

• practice — not a real PYQ

  Which is the primary payload of the Aditya-L1 mission ?

  • (a)Solar Ultraviolet Imaging Telescope (SUIT)
  • (b)Visible Emission Line Coronagraph (VELC)
  • (c)Plasma Analyser Package for Aditya (PAPA)
  • (d)Aditya Solar wind Particle Experiment (ASPEX)

  Answer(b) Visible Emission Line Coronagraph (VELC) — built by the Indian Institute of Astrophysics, Bengaluru, for imaging and spectroscopy of the solar corona.