The L1 point is not a point as much as a small region in space. It has been host to multiple solar weather monitoring and science observation missions in the past, such as SOHO, ACE, WIND, DSCOVR, etc. Aditya-L1 will be different because it will observe the Sun in multiple wavelengths, like how Astrosat observes the universe. And its observations will complement data from the NASA Parker Solar Probe.
The hope is to explain why the Sun’s corona is hotter than its surface by several million degrees. This is a major unsolved problem in solar physics.
4. Specialised X-ray observatory
ISRO will be launching another space science mission, called X-ray Polarimetry Satellite (XPoSat), onboard a PSLV in 2021. Unlike the Swiss Army knife that is Astrosat, XPoSat will be a specialised science mission that will study the polarisation of X-rays in space. How radiation is polarised gives away the nature of its source, including the strength and distribution of its magnetic fields and the nature of other radiation around it.
To this day, the Crab Nebula remains the only X-ray source for which scientists have measured the polarisation. XPoSat is expected to provide the same information about the 50 brightest known sources in the universe, including pulsars, X-ray binary stars and galactic cores.
XPoSat’s polarimeter instrument, which works in the medium X-ray region (8-30 keV), is being built and tested by scientists at the Raman Research Institute. It is delightful to have Indian space missions fill humanity’s gaps in its knowledge of astrophysics.
Like Astrosat, XPoSat will be placed in a low-Earth orbit.
5. A Venus orbiter in the making
Last year, ISRO called for payload proposals for a Venus orbiter mission to be launched in 2023. This is great because an initial interest in exploring the planet, in the 1960s and 1970s, quickly faded after Mars started getting all the attention.
Right now, there is only one spacecraft at Venus, the Japanese orbiter Akatsuki, compared to eight at Mars. So ISRO sending a mission to Venus should be refreshing for the global planetary science community.
Together with the difficult space environment and the planet’s notoriously hostile environment, there have been few missions to Venus in the last four decades, leaving us in the dark about Earth’s twin.
ISRO’s Venus orbiter is expected to have a payload capacity of 100 kg and will be placed in a highly elliptical orbit, of 500 ✕ 60,000 km, for closeup and global observations, respectively. In addition to the room for 12 Indian instruments, ISRO will also be able to add a few international ones.
Its primary scientific objectives include surface and subsurface feature studies, atmospheric chemistry and solar wind interactions. NASA has already expressed interest in sending a terahertz instrument onboard the orbiter to see through Venus’s thick atmosphere and observe chemical reactions below.
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Other missions in ISRO’s pipeline include follow-ups to the Mars Orbiter Mission, Astrosat and Chandrayaan 2, all before 2025. Given ISRO’s fairly nascent space science program, the boost to such missions as discussed in its annual report only bodes well for the Indian space programme.
Jatan Mehta is a science writer with a background in physics and research experience in astrophysics. He is passionate about space, technology and science communication. His portfolio is at jatan.space.