Tag: synthetic aperture radar

• Robbing NISAR to pay ISRO

  A.K. Anil Kumar, the director of ISRO’s Telemetry, Tracking, and Command Network (a.k.a. ISTRAC), has reportedly made some seriously misleading comments as part of his convocation address at a Maharishi University in Lucknow.* Kumar’s speech begins at the 1:38:10 mark in this video (hat-tip to Pradx):

  A poorly written article in The Free Press Journal (which I couldn’t find online) has amplified Kumar’s claims without understanding that the two satellites Kumar was seemingly talking about are actually one: the NASA-ISRO Synthetic Aperture Radar (NISAR), developed jointly by the US and Indian space agencies. The article carries an image of NISAR but doesn’t caption it as such.

  

  The article makes several dubious claims:

  • That the “satellite” can forecast earthquakes,
  • That NISAR can capture subsurface images of Earth, including of underground formations,
  • That India’s “satellite” didn’t require a 12-metre-long antenna the way NASA’s “satellite” did, and
  • That ISRO’s “satellite” was built at one-tenth of the cost of NASA’s “satellite”

  To be clear, an ISRO satellite that can forecast earthquakes or image subsurface features and which the organisation built and launched for Rs 1,000 crore does not exist. What actually exists is NISAR, a part of which ISRO built. The claims are almost spiteful because they purport to come from a senior ISRO official whose work likely benefited from the ISRO-NASA collaboration and because he ought to have known better than to mislead.

  NISAR is a dual-frequency (DF) synthetic aperture radar (SAR). The ‘DF’ bit means the satellite captures data on two radar frequencies, L-band and S-band. To quote from a piece I wrote for The Hindu on July 27:

  At the time the two space organisations agreed to build NISAR, NASA and ISRO decided each body would contribute equivalent‑scale hardware, expertise, and funding. … [ISRO] supplied the I‑3K spacecraft bus, the platform that houses the controls to handle command and data, propulsion, and attitude, plus 4 kW of solar power. The same package also included the entire S‑band radar electronics, a high‑rate Ka‑band telecom subsystem, and a gimballed high‑gain antenna.

  ‘SAR’ refers to a remote-sensing technique in which a small antenna moves along a path while using a computer to combine the data it captures along the way, thus mimicking a much larger antenna. NISAR uses a 12-metre mesh antenna plus a reflector for this purpose. Both the S-band and L-band radars use it to perform their functions. As a result of using the SAR technique, the two radars onboard NISAR are able to produce high-resolution images of Earth’s surface irrespective of daylight or cloud cover and support studies of ground deformation, ice sheets, forests, and the oceans.

  In this regard, for The Free Press Journal to claim NISAR “didn’t require India to install a separate 12-metre antenna, unlike NASA” gives the impression that ISRO’s S-band radar didn’t need the antenna. This is wrong: it does need the antenna. That NASA was the agency to build and deploy it on NISAR comes down to the terms of the collaboration agreement, which specified that ISRO would provide the spacecraft bus, the S-band radar (and its attendant components), and the launch vehicle while NASA would take care of everything else. This is the same reason why ISRO’s contributions to NISAR amounted to around Rs 980 crore — which Kumar rounded up to Rs 1,000 crore — whereas NASA’s cost was around Rs 10,000 crore.

  The antenna is in fact an engineering marvel. Without it ISRO’s S-band radar wouldn’t be so performant and thus its data wouldn’t be so useful for decision-making for both research and disaster management. On the day ISRO launched NISAR, on July 30 this year, I got to interview Karen  St. Germain, the director of the Earth Science Division at the Science Mission Directorate at NASA. Here’s an excerpt from the interview about the antenna:

  Both the L-band and the S-band radars use the same reflector. Since S-band has a shorter wavelength than the L-band, does this create any trade-offs in either L-band or S-band performance?

  It doesn’t. And the reason for that is because this is a synthetic aperture radar. It creates its spatial resolution as it moves along. Each radar is taking snapshots as it moves along. You know, to get this kind of centimetre level fidelity and the kind of spatial resolution we’re achieving, if you were to use a solid antenna, it would have to be five miles long. Just like when you’re talking about a camera, if you want to be able to get high fidelity, you need a big lens. Same idea. But we can’t deploy an antenna that big. So what we do is we build up image after image after image to get that resolution. And because of this technique, it’s actually independent of wavelength. It works the same for S- and for L-bands. The only thing that’s a little different is because the antenna feeds for the L-band and the S-band can’t physically occupy the same space, they have to be next to each other and that means there’s a slight difference in the way their pulses reflect off the antenna. There’s that positioning difference, and that we can correct for.

  Could you tell us a little bit more about that slight difference?
  
  Karen St. Germain: It’s the way a reflector works. You would ideally want to put the feed at the focal point of the reflector. But when you have two feeds, you can’t do that. So they’re slightly offset. That means they illuminate the reflector just slightly differently. The alignment is just a little bit different. The team optimised the design to minimise that difference and to make it so that they could correct it in post-processing.

  And even for all these abilities, we (i.e. people everywhere) currently don’t know enough to be able to forecast earthquakes. What we can do today is make short-term predictions and we can prepare probabilistic forecasts over a longer period of time. That is, for instance, we can say “there’s a 20% chance of a quake of magnitude 8 or more occurring in the Himalaya in the next century” and we have the means to alert people in an area tens of seconds before an earthquake occurs. We can’t say “there will be an earthquake in Chennai at 3 pm tomorrow”.

  The question for The Free Press Journal is thus what role a satellite can essay in this landscape. In a statement in 2021, ISRO had said “NISAR would provide a means of disentangling highly spatial and temporally complex processes ranging from ecosystem disturbances to ice sheet collapses and natural hazards including earthquakes, tsunamis, volcanoes and landslides.” This means NISAR will help scientists better piece together the intricate processes implicated in earthquakes — processes that are distributed over some area and happen over some time. Neither NISAR nor the S-band radar alone can forecast earthquakes.

  On a related note, the L-band (1,000-2,000 MHz) and S-band (2,000-4,000 MHz) radar frequencies do overlap with the frequencies used in ground-penetrating radar (10-4,000 MHz). However, the lower the frequency, the further underground an electromagnetic wave can penetrate (while keeping the resolution fixed). Scientists have documented a ceiling of around 100 MHz for deep geological profiling, which is far from either of NISAR’s radars. Even the L-band radar, which has lower frequency than the S-band, can at best penetrate a few metres underground if the surface is extremely dry, like in a desert, or if the surroundings are made of water ice. What both radars can penetrate very well is cloud cover, heavy rain, and vegetation.

  The ISRO + NASA collaboration that built NISAR was a wonderful thing that the agencies need to replicate in future even as it continued their less formalised engagements from before and whose benefits both host countries, India and the USA, continue to accrue in the satellite observation and remote-sensing domains. For Kumar to call the cost component into question in the way that he did, followed by the The Free Press Journal‘s shoddy coverage of his remarks, does no favours to the prospect of space literacy in the country.

  * I updated this post at 7.45 pm on December 2, 2025, to make it clear that all but one of the objectionable claims were made by The Free Press Journal in its article; the exception was the cost comparison, which Kumar did make.

  2025.12.02

• Frugality is a toxic chalice

  From ‘Earth Imaging Satellite NISAR Exposes NASA’s Weaknesses, ISRO’s Strengths’, NDTV, July 26, 2025:

  At the end of the day, the US scientists have swallowed their pride and are sheepishly going to watch the launch of a satellite where they have invested nearly $1.15 billion. It is this exorbitant cost by NASA that should also be a reason for Americans to squirm and be uncomfortable.

  When ISRO’s Mars Orbiter Mission entered into orbit around Mars, The New York Times carried a cartoon showing a dhoti-clad man holding a cow in one hand and knocking with the other asking to be let into a room where he could sit with the world’s other major space powers. The paragraph above as well as many others in the NDTV article are simply the other side of the same coin: one cast ISRO as a frugal simpleton and the other takes exorbitant pride in ISRO’s frugality.

  If it isn’t clear by now, however, ISRO’s lower costs stem from the fact that it’s simply underfunded and its staff underpaid. ISRO has spent less than other space agencies but how similar are the corresponding missions? The organisation’s payloads are often much lighter, carry fewer instruments, and are less capable of cutting edge science. The bigger story is that ISRO is trying (and which could be even bigger if there was a long-term plan that showed how all the smaller scale attempts added up). However, it’s not that ISRO is doing what NASA is because it simply isn’t.

  There is no reason for NASA to squirm and be uncomfortable, either: the cost reflects the strength of the US dollar and the organisation of the US economy. It also accounts for NASA being responsible for receiving, processing, distributing, and archiving NISAR data for the whole world, whereas ISRO is responsible for doing the same thing only vis-à-vis India.

  The NDTV article goes on to say:

  There are many reasons behind the huge cost incurred by NASA, one of them being that most of the development of the instruments and payloads they fly are made by huge multi-national corporations and they not only need huge profits but also need to share dividends with their share-holders. ISRO, on the other hand, being a national entity does these things in-house and has no reason to pad up the cost to share profits with share-holders.

  NASA’s principal contribution to NISAR was the L-band synthetic aperture radar (SAR) and the associated avionics and the 12-m mesh antenna plus the 9-m boom holding it. All these components were made at NASA’s Jet Propulsion Laboratory, just as ISRO’s contributions onboard NISAR came from its Space Applications Centre in Ahmedabad.

  Additionally, an ISRO official said that when their scientists travel to the Jet Propulsion Laboratory in Pasadena in California, they would stay in shared $100 a day room while the NASA scientists when they travel to the UR Rao Satellite Center in Bengaluru would stay in an over $500 a day room. This automatically inflates the costs.

  We’re talking about a monetary difference of more than 10x between nine- and ten-digit figures. I highly doubt that a small group of scientists staying for N number of days in $500 rooms could make much of a difference. Even if these costs added up in the alleged manner, living comfortably in clean environs is more important than roughing it out to save pennies. I’m also tempted to say that rooms and kitchens in cheaper hotels in the US are likely cleaner than most hotels in India.

  Also, India usually makes only one instrument the one that will fly into space, while NASA makes an engineering model and flight model, which leads to doubling the cost.

  It increases the cost. However, the engineering model is a fully functional hardware unit that can be subjected to full-scale integration testing without risking the actual flight unit. Teams can also work on software development, system integration, and ground testing in parallel while the flight model is still being assembled, avoiding bottlenecks and improving the flight model’s build. If an issue arises after launch, engineers on the ground replicate the problem on the engineering model before trying fixes on the actual spacecraft — an ability that came in handy during the Boeing Starliner crewed flight test. Finally, the engineering model is subjected to more aggressive and destructive testing, and what engineers learn they use to improve the flight model, increasing the chances that it will succeed. In the end, for the additional cost, NASA is able to send better instruments to space that operate within narrower margins of error.

  The funny thing is ISRO may also have to switch to similar developmental processes in future as it embarks on more sophisticated projects, including interplanetary sample-return missions and crewed lunar landings. I hope ISRO, unlike NDTV, isn’t taking overmuch pride in its supposed frugality.

  The way human power is distributed is also very different between NASA and ISRO at the Indian space agency. In the case of NISAR, which has taken over 11 years to build, the teams at ISRO working on multiple satellites and the salaries in India also turn out to be much lower when converted into dollar terms. The top manager at ISRO also pointed out that ISRO engineers are willing to put in long hours and work over weekends, while the US contract engineers are reluctant to put in long hours.

  Don’t just convert it into dollar terms. Also check whether the values of each work-hour with respect to the national economy in the two countries are comparable. Short of that, let’s avoid such comparisons altogether.

  There’s also more than meets the eye in valorising people being “willing” to put in longer hours and to work over the weekends while diminishing a person’s reluctance to do so. In fact, there’s a thin line between a person volunteering to put in extra and a person being expected to put in extra. I’ve seen firsthand company cultures veering over time to make the latter a foundational expectation, with managers often justifying it by saying things like “this is what it takes”, “do it for the <insert cause here>”, and “if you don’t want to, you’re in the wrong industry”. It is a worker’s right to limit their working hours to the stipulated ones. If India’s satellites are cheaper because ISRO is overworking its labour force, we’re doing it wrong — and the bill will soon come due.

  The premium for insurance also adds to the costs at ISRO since the government takes the full liability and no insurance is taken. In other countries, insurance premiums can be a huge cost. Incidentally, when India launched its communication satellite using the SpaceX Falcon-9 rocket, India also took insurance.

  NISAR costs around $1.5 billion. If I’m not mistaken, launch insurance typically costs 15-25% of the total insured value, which is the cost to replace the satellite and to launch it. In this case that would be $225-375 million. After launch coverage expires (which is when the satellite completes one year in orbit), the annual in-orbit insurance usually costs 1-3% per year, which is around $15-45 million a year. Given NISAR’s expected lifetime of three years, the total insurance cost could be $255-465 million; if we go by NISAR’s design lifetime of five-plus years, it could come to $285-555 million.

  The NDTV article also calls out the irony inherent to a NASA satellite scheduled to lift off onboard a GSLV Mk-II rocket. To the uninitiated: this is deserved because the US government scuttled a deal in the early 1980s for the Soviet Union to transfer cryogenic engine technology to India. India was subsequently forced to develop the engines on its own by taking apart and studying the Soviet engines it was able to buy, ultimately building the machine that powers the third stage of the GSLV Mk-II. (Edit: updated at 8.43 pm on July 31, 2025, from “fourth” to “third” stage.) However, the narrative goes on:

  Some would say this is an irony of ironies, and some would say it is egg on the face of US.

  Unless the article could quote someone (by name) actually making these claims, the strength of language in the second half of the statement is unfounded. In fact, the author may have been better off staking the claim themselves — “I believe this is egg on the US’s face” — but even then they will have to justify how it can be reconciled with several changes in NASA’s and the US’s leadership as well as policies regarding working with ISRO/India since the 1980s.

  ---

  Rather than concern ourselves with superficial one-upmanship, we would be better off discussing the demands of the different realities of ISRO and NASA. Both organisations have made conscious choices to develop spacecraft the way they do. Their needs are different and their political-economic contexts are wildly different. Expenditure and achievement may not be directly related because material and labour costs are lower in India yet they are deeply connected to an ambition mismatch as well. In order for ISRO to contribute Rs 800 crore to a climate-focused Earth-observing mission, (i) NASA had to conceive of NISAR based on climate scientists’ inputs and (ii) spend $1.1 billion of its own for the L-band SAR and the giant antenna, without which even ISRO’s S-band SAR wouldn’t have the resolution and swath width it currently does. But to be sure: one’s ambitions are not ‘greater’ than the other’s; they’re just different.t

  It also matters that, leading up to the launch, NASA officials and scientists have embarked on a media blitz. It’s proving really easy right now to catch hold of a NASA scientist for an extended interview on NISAR — but not an ISRO scientist.

  For all these reasons, it’s always more sensible to celebrate ISRO in terms that don’t invoke rupees or by comparing and contrasting its feats with that of another space agency.

  2025.07.28

• A new map of Titan

  It’s been a long time since I’ve obsessed over Titan, primarily because after the Cassini mission ended, the pace of updates about Titan died down, and because other moons of the Solar System (Europa, Io, Enceladus, Ganymede and our own) became more important. There have been three or four notable updates since my last post about Titan but this post that you’re reading has been warranted by the fact that scientists recently released the first global map of the Saturnian moon.

  

  (This Nature article offers a better view but it’s copyrighted. The image above is a preview offered by Nature Astronomy; the paper itself is behind a paywall and I couldn’t find a corresponding copy on Sci-Hub or arXiv nor have I written to the corresponding author – yet.)

  It’s fitting that Titan be accorded this privilege – of a map of all locations on the planetary body – because it is by far the most interesting of the Solar System’s natural satellites (although Europa and Triton come very close) and were it not orbiting the ringed giant, it could well be a planet of its own accord. I can think of a lot of people who’d agree with this assessment but most of them tend to focus on Titan’s potential for harbouring life, especially since NASA’s going to launch the Dragonfly mission to the moon in 2026. I think they’ve got it backwards: there are a lot of factors that need to come together just right for any astronomical body to host life, and fixating on habitability combines these factors and flattens them to a single consideration. But Titan is amazing because it’s got all these things going on, together with many other features that habitability may not be directly concerned with.

  While this is the first such map of Titan, and has received substantial coverage in the popular press, it isn’t the first global assessment of its kind. Most recently, in December 2017, scientists (including many authors of the new paper) published two papers of the moon’s topographical outlay (this and this), based on which they were able to note – among other things – that Titan’s three seas have a common sea level; many lakes have surfaces hundreds of meters above this level (suggesting they’re elevated and land-locked); many lakes are connected under the surface and drain into each other; polar lakes (the majority) are bordered by “sharp-edged depressions”; and Titan’s crust has uneven thickness as evidenced by its oblateness.

  According to the paper’s abstract, the new map brings two new kinds of information to the table. First, the December 2017 papers were based on hi- and low-res images of about 40% of Titan’s surface whereas, for the new map, the authors write: “Correlations between datasets enabled us to produce a global map even where datasets were incomplete.” More specifically, areas for which authors didn’t have data from Cassini’s Synthetic Aperture Radar instrument for were mapped at 1:2,000,000 scale whereas areas with data enabled a map at 1:8,000,000 scale. Second is the following inferences of the moon’s geomorphology (from the abstract the authors presented to a meeting of the American Astronomical Society in October 2018):

  We have used all available datasets to extend the mapping initially done by Lopes et al. We now have a global map of Titan at 1:800,000 scale in all areas covered by Synthetic Aperture Radar (SAR). We have defined six broad classes of terrains following Malaska et al., largely based on prior mapping. These broad classes are: craters, hummocky/mountainous, labyrinth, plains, lakes, and dunes [see image below]. We have found that the hummocky/mountainous terrains are the oldest units on the surface and appear radiometrically cold, indicating icy materials. Dunes are the youngest units and appear radiometrically warm, indicating organic sediments.

  

  More notes once I’ve gone through the paper more thoroughly. And if you’d like to read more about Titan, here’s a good place to begin.
  

  2019.11.19