X-SAT

X-SAT (also catalogued as X-Sat) is a Singaporean microsatellite developed through a collaboration between Nanyang Technological University (NTU) and the Defence Science and Technology Agency's research arm, the Defence Science Organisation (DSO) of Singapore. Assigned NORAD catalog ID 37389 and international designator 2011-015C, the spacecraft was launched in April 2011 as part of a multi-payload mission aboard an Indian Space Research Organisation (ISRO) rocket. It remains in orbit today, circling Earth in a near-polar sun-synchronous trajectory at altitudes between approximately 802 and 822 kilometres.

Mission and Purpose

The precise operational goals of X-SAT are not fully detailed in publicly available catalog records, and its mission type and current operational status are not confirmed in the tracking data. What is known from the programme's background is that the satellite was conceived as an exercise in indigenous spacecraft development — an effort by Singapore to build meaningful in-house capability in satellite design, engineering, and fabrication rather than simply procuring a finished platform from an established space contractor.

Microsatellites of this class — generally defined as spacecraft with masses on the order of tens of kilograms — are commonly used for Earth observation, technology demonstration, and educational or research purposes. The involvement of NTU, a research-intensive university, alongside DSO, which focuses on applied defence science and technology, suggests the programme had both an academic training dimension and a broader national interest in establishing technical foundations for future space endeavours. Whether the satellite carried specific imaging payloads, experimental instruments, or a combination of both has not been confirmed in the object's public catalog entry.

The satellite was launched alongside two other spacecraft: India's ResourceSat-2, a well-known Earth observation satellite operated by ISRO, and YouthSat, a joint Indo-Russian scientific mission focused on studying the upper atmosphere and ionosphere. The shared launch context places X-SAT within a broader cooperative framework in which smaller national programmes benefit from rideshare opportunities on proven launch vehicles.

Orbit and Tracking

X-SAT operates in a sun-synchronous orbit (SSO), a type of near-polar, low Earth orbit in which the orbital plane maintains a roughly constant angle relative to the Sun throughout the year. This is achieved by selecting an inclination slightly greater than 90 degrees — in X-SAT's case, 98.4° — which causes the orbital plane to precess in sync with Earth's revolution around the Sun. The result is that the satellite passes over any given point on Earth at approximately the same local solar time on each successive pass, a property that makes sun-synchronous orbits especially valuable for Earth observation, since lighting conditions remain consistent from one image to the next.

Current tracking data places X-SAT's apogee at 822 kilometres and its perigee at 802 kilometres, giving it a nearly circular orbit with only about 20 kilometres of variation between its highest and lowest points. The satellite completes one full revolution around Earth approximately every 101.0 minutes, meaning it makes roughly 14 to 15 orbits per day. Over the course of each day, the slight shift in ground track between successive passes allows the satellite's ground track to gradually cover different swaths of Earth's surface.

With a NORAD ID of 37389 and international designator 2011-015C, X-SAT is routinely tracked by the United States Space Surveillance Network and its orbital elements are updated and published in two-line element (TLE) sets accessible through space-tracking services including this catalogue. The object type is classified as PAYLOAD, distinguishing it from the rocket bodies and debris associated with its launch. As of the time of writing, the satellite has not undergone atmospheric reentry and remains an active tracked object in low Earth orbit.

At these altitudes — roughly 800 kilometres above the surface — aerodynamic drag is extremely low but not entirely absent. Objects in this altitude band can remain in orbit for decades before orbital decay brings them back into the denser atmosphere. The nearly circular nature of X-SAT's orbit suggests it has experienced relatively little differential drag-induced deformation since its insertion.

Design and Operator

X-SAT was developed by NTU in collaboration with DSO Singapore, representing a significant institutional investment in building domestic space engineering capability. The manufacturer of specific subsystems or the spacecraft bus itself is not recorded in the public tracking catalog, and the satellite's mass is similarly not confirmed in available data.

NTU is one of Asia's leading research universities and has maintained an active interest in small satellite programmes as a means of providing hands-on engineering experience for students and researchers while simultaneously advancing Singapore's national technological profile. DSO, for its part, operates as the primary defence research and development organisation in Singapore, working on technologies relevant to national security applications. The collaboration between an academic institution and a defence research body on a space programme is a model used in several countries to accelerate capability development while distributing technical expertise across sectors.

The spacecraft was launched on ISRO's Polar Satellite Launch Vehicle, in the configuration designated PSLV-C16, lifting off from the First Launch Pad (FLP) at Satish Dhawan Space Centre, located on Sriharikota Island off the eastern coast of India. The launch took place on 20 April 2011. ISRO's PSLV has become one of the more reliable and commercially sought-after medium-lift launch vehicles in the world, with a track record of successfully deploying multiple payloads — including numerous foreign microsatellites — into sun-synchronous and other low Earth orbits. The use of PSLV for X-SAT's launch reflects the practical reality that Singapore, at the time of the mission, lacked its own indigenous launch infrastructure and relied on an established international partner to place the satellite into its intended orbit.

The satellite is operated under the authority of the Singapore government, making it a nationally owned and government-operated asset, even if the day-to-day technical operation may be managed through NTU or DSO facilities.

Significance and Legacy

X-SAT holds a notable place in Singapore's space history as one of the country's early dedicated satellite programmes developed with substantial domestic engineering involvement. For a small, highly urbanised city-state with no indigenous launch capability and limited physical geography, the decision to invest in satellite development represented a deliberate strategic choice to participate meaningfully in the space sector rather than remain purely a consumer of space services and data.

The programme demonstrated that Singapore's engineering institutions were capable of designing and constructing a satellite to a standard sufficient for orbital deployment — a non-trivial accomplishment given the demanding requirements of the space environment, where components must survive vacuum, thermal cycling, radiation exposure, and the mechanical stresses of launch without the possibility of in-orbit maintenance or repair.

In the broader regional context, X-SAT was part of a wave of small satellite programmes undertaken by Asian nations in the 2000s and early 2010s, many of which used microsatellites as a cost-effective entry point into space activities. These programmes served dual purposes: building technical human capital and signalling national ambition in a domain increasingly recognised as strategically important for communications, surveillance, navigation, and environmental monitoring.

Since X-SAT's launch, Singapore has continued to develop its space sector, with subsequent satellite projects building on the experience accumulated through programmes like X-SAT. The satellite itself continues to orbit Earth more than a decade after its launch, a testament to the durability of well-engineered small spacecraft deployed at altitudes where atmospheric drag is minimal.

The mission and operational status of X-SAT are not publicly confirmed in available catalog data, so it is not possible to state with certainty whether the satellite is still actively transmitting or performing any function, or whether it has transitioned to a passive derelict status. Regardless of its current operational condition, its presence in the catalog as a tracked payload attests to its continued physical existence in orbit.

How to Spot It

X-SAT orbits at an altitude of roughly 802 to 822 kilometres in a sun-synchronous orbit inclined at 98.4°, which means its ground track covers virtually all latitudes up to approximately 98 degrees — effectively the entire populated surface of Earth. As a microsatellite, it is not among the brighter objects visible to the naked eye, and casual skywatchers are unlikely to pick it out without optical aid. However, observers equipped with binoculars and access to up-to-date TLE data can, in principle, attempt to locate it during passes when the satellite is illuminated by sunlight while the observer is in twilight or darkness. Dedicated satellite-tracking software using the current orbital elements published on this site will yield the most accurate predictions for pass times and sky positions for any given location.