Spies in the skies

“Spies in the skies” wasn’t actually the title of the talk given by HEO’s Toby Harris and Hannah Dawe at the Royal Aeronautical Society this week, but it was all I could think about afterwards.

HEO’s stated goal is to “image anything in the solar system, on demand” (though on further questioning it became clear this was more ‘catchy tagline’ than serious intention to image gas giants).

Their service offers customers the chance to get images of objects in space using existing space assets, such as Earth observation satellites. These images can help customers identify issues with the space hardware, characterise space debris for better debris-removal mission design, calculate tumble rates ahead of re-entry, or, of course, check out what another country has just launched.

How does it work?

HEO has access to around 35 EO satellites that can be used to capture images of items in space when the target objects cross their path. As space gets more congested, space situational awareness is increasingly important. Objects in space are meticulously tracked so that collision avoidance manoeuvres can be taken if two objects get a bit too close for comfort. HEO makes use of this tracking data to work out when a target object will (at a safe distance) cross the path of an EO satellite in its network. When it does, they can task the EO satellite to point in the target’s direction, image it, and send back images for their customers.

It’s not quite as simple as taking a snap any time an object is close enough. HEO’s customer needs are not the prime mission of the EO satellites, so images need to be taken in their ‘down-time’. You also have to consider the angle of the Sun to ensure that your target is well lit for the best picture. (It can sometimes be useful to get a silhouette of an object as this could give you information about its attitude ahead of re-entry, for example, but in general they want objects to be reflecting sunlight.)

Customers request images of an object, and HEO checks for suitable conjunctions. Depending on conjunction timing, angle of the Sun, and distance, they select the best satellite and task it to take photos. It usually takes between 24-72 hours to find a suitable conjunction and images are with the customer within 24 hours of them being downlinked.

Non-Earth Imaging (NEI)

The company originally wanted to image near-Earth objects to learn more about them and characterise them for mining, but as Toby, HEO Director of Space Applications, admitted, both the imaging and mining ideas turned out to be hard.

The space-to-space imaging they now offer is focussed on delivering non-Earth imaging (NEI) of objects such as satellites, rocket bodies, and space stations. Analysis is carried out to determine size, geometry and configuration, and also help to determine the object’s intended use. The company can also construct 3D models of objects based on captured images and available open-source data.

By taking multiple images of the Chinese space station Tiangong, while it was being built for example, HEO was able to build up a 3D model showing how different modules were brought together during station construction.

Dual use

Not only does the HEO approach create a dual purpose for existing satellites, it can also be used for both civil and military purposes. On the civil side, it could help satellite operators check the status of their hardware, check for debris after deployment, predict re-entry locations or to de-risk active debris removal – all things that Toby and Hannah were keen to highlight. But the military applications are hard to ignore.

With visible and multispectral sensors, NEIs could help military agencies and governments get a close-up look at what competitors have put in space – gauging the form, function and physical make-up of their assets. Inevitably military space assets from countries like the US will have already had this capability, but HEO claims to be offering the world’s first commercial in-orbit satellite inspection software programme – and anyone can sign up for an account.

This raises some questions. As a commercial company, how does HEO balance the need for commercial income, with security concerns from competing national customers? Hypothetically, if Russia wished to buy images of US assets, and money wasn’t an issue, would HEO fulfil the request? Toby’s response was that if they did, they’d not get much business from the US again. That makes sense, but what about less clear-cut situations?

And what of the satellite owners and operators? Do they know who the end customer is? Can they opt out of military requests? This is probably less of an issue for commercial satellites, but if HEO wants to grow its network and coverage, it could be a blocker to using satellites owned by civil space programmes.


I was also keen to know where liability would lie if an EO satellite was damaged in the course of taking an image for an HEO customer. If the satellite was turned to face a target object and a sensor got frazzled by the Sun for example, would HEO be liable for the loss? Are they insured? (On that point Toby wasn’t 100% clear – but pointed out that while they make the task requests, they are never operating the EO satellite themselves.)

On the flip-side, could space-to-space imaging be used to determine liability in the case of an accident in space? Or to check that space players are meeting their obligations to reduce space debris?

Future goals

HEO has developed its own sensor payloads – Holmes and Adler – that can be launched on 3rd party satellites. Holmes 1 and 2 have already been launched, and the company aims to increase its available coverage.

Currently they can image objects up to 800km altitude, and cover two-thirds of LEO, with full coverage planned by 2025. Objects in High LEO and GEO are visually unmonitored, but HEO is planning missions to allow imaging in these orbits in 2025.

HEO services could be a huge help for active debris removal missions. Being able to check the state and shape of the object you want to de-orbit, as well as its tumble rate, would help de-risk missions.

HEO was used to image the European Remote Sensing 2 (ERS-2) satellite during its recent re-entry. It is hoped that combining in-space images with data from ground-based sensors could lead to more accurate re-entry predictions in future.

The use of existing space assets has allowed HEO to develop a product without taking on the risk and cost of launching its own network of satellites. It’s smart to use EO satellites when they are not taking images for their primary mission and helps us to get the maximum benefit of satellites without further adding to the congestion of space.

Whatever the customers’ reason for using the service – inspecting faulty satellites, characterising space debris, predicting re-entry profiles or spying on your competitors – securing access to a network of EO satellites to deliver it is impressive.

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