CDS (II) 2020 General Knowledge · Question 85 of 120

Correct — D, 6. Pragyan, the rover carried by Chandrayaan-2, ran on six wheels. It was a small machine — about 27 kg, drawing 50 watts from a solar panel, moving at roughly one centimetre a second with a planned range of 500 metres, and designed to work for a single lunar day of about fourteen Earth days, since its electronics could not survive the lunar night. Six wheels is the standard configuration for a planetary rover because a six-wheel rocker-bogie suspension keeps every wheel on the ground over rough, loose regolith and lets the vehicle climb obstacles taller than a wheel without tipping. Pragyan never rolled, however: the Vikram lander deviated from its descent path and crashed on 6 September 2019, destroying the rover with it. The orbiter, the third element of the mission, survived and continues to work.

• (a)2 — Two wheels could not keep a vehicle upright on loose lunar soil, and gives no redundancy at all if one motor fails.
• (b)3 — Three wheels is a stable geometry on a flat floor but useless on regolith with rocks and slopes, where the load must be spread and each wheel needs independent travel.
• (c)4 — Four is a reasonable guess by analogy with a car, and it is the commonest wrong answer, but planetary rovers from Lunokhod and Apollo onwards have used six or more for traction and redundancy.

Chandrayaan-2 was launched on 22 July 2019 on the GSLV Mk III-M1, now designated LVM3, from Satish Dhawan Space Centre at Sriharikota. It had three parts: an orbiter, the Vikram lander and the Pragyan rover. The spacecraft entered lunar orbit on 20 August 2019; the landing attempt failed in the small hours of 7 September when Vikram lost its trajectory below about 2.1 km. The orbiter remains operational and continues to return data. The follow-up mission, Chandrayaan-3, carried a lander and rover of the same names, launched on 14 July 2023 on LVM3-M4 and soft-landed near the lunar south pole on 23 August 2023, making India the fourth country to soft-land on the Moon and the first at the south pole. The landing site was named Shiv Shakti Point and 23 August is now observed as National Space Day.

The question is a hardware detail, and hardware details are best remembered through the reason behind them. A rover on regolith needs many small wheels rather than few large ones, so that weight is spread and no single failure strands the vehicle, and six is the number the rocker-bogie design settles on. It is also worth keeping the two missions apart, since both carry a Vikram and a Pragyan. The 2019 rover was lost on landing; the 2023 rover of the same name is the one that actually drove on the Moon, covering just over a hundred metres before lunar night fell.

• Pragyan, the Chandrayaan-2 rover, had six wheels, weighed about 27 kg and drew 50 W from solar panels.
• It was designed to travel at about 1 cm per second up to a range of 500 m, for one lunar day of about fourteen Earth days.
• Chandrayaan-2 launched on 22 July 2019 on GSLV Mk III-M1 and entered lunar orbit on 20 August 2019.
• The Vikram lander crashed on 6-7 September 2019 and the rover was lost with it; the orbiter remains operational.
• Chandrayaan-3, launched 14 July 2023 on LVM3-M4, soft-landed near the lunar south pole on 23 August 2023; the site is Shiv Shakti Point and the date is now National Space Day.

• Guessing four wheels by analogy with a car.
• Mixing up the two missions. Vikram and Pragyan are the names used for both the 2019 and the 2023 lander and rover.
• Saying Chandrayaan-2 failed entirely. The lander was lost, but the orbiter is still working.

As a hardware-detail item on a named mission, or as a mission-to-launch-vehicle or mission-to-date match.

• practice — not a real PYQ

  The lander of the Chandrayaan-2 mission was named

  • (a)Pragyan
  • (b)Vikram
  • (c)Aditya
  • (d)Bhaskara

  Answer(b) Vikram — Pragyan was the rover it carried; both names were reused for Chandrayaan-3.

• practice — not a real PYQ

  Chandrayaan-2 was launched using which launch vehicle?

  • (a)PSLV-C11
  • (b)GSLV Mk II
  • (c)GSLV Mk III-M1
  • (d)SSLV-D1

  Answer(c) GSLV Mk III-M1 — now designated LVM3, launched from Satish Dhawan Space Centre on 22 July 2019.