Synchronous orbit: An orbit whose period is a rational multiple of the average rotational period of the body being orbited and in the same direction of rotation as that body. This means the track of the satellite, as seen from the central body, will repeat exactly after a fixed number of orbits. In practice, only 1:1 ratio (geosynchronous) and 1:2 ratios (semi-synchronous) are common. A visualization of satellites, debris, and other objects tracked by LeoLabs in low earth orbit. LeoLabs Explore LEO LEO Catalog Today's Conjunctions Catalog Search Constellations Instrument Sites System Metrics Documentation Getting Started Guide CLI Docs API Docs. Characteristics of LEO Systems. “Anytime, Anywhere”. Blends cellular and satellite technologies – Satellite – Terrestrial – Gateways. 500 - 2000 km orbit – Below Van Allen Belts. Fiber-like propagation delay. Voice and data capabilities. Hand-held multi-mode phones. This article is based on the paper “Precise Onboard Orbit Determination for LEO Satellites with Real-Time Orbit and Clock Corrections” presented at ION GNSS+ 2016, the 29th International Technical Meeting of the Satellite Division of The Institute of Navigation, held Sept. 12–16, 2016, in Portland, Oregon. A visualization of satellites, debris, and other objects tracked by LeoLabs in low earth orbit. LeoLabs Explore LEO LEO Catalog.

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The USA have for a long time been trying to track missiles after the main engine has burned out. The recent rise of manoeuvrable hypersonic gliders and cruise missiles has made this need more pressing, since they fly very low compared to ballistic missiles, and consequently they are mostly below the radar horizon.

China and Russia are developing such weapons, and since according to US generals “there are not enough islands in the Pacific to place enough radars to get a good coverage”, the solution for tracking them will have to come from space.

As demonstrated in the article Detecting hypersonics, if you do not have a sensor able to detect and track the missiles over an Earth background, then you need an extremely large number of satellites: at least 16 in GEO, and much more if using lower orbits. The Pentagon has arrived to a similar conclusion, and financed the development of the SBTSS below-the-horizon sensor. They do note, however, than extracting the faint signal from the background clutter caused by Earth’s surface is one of the toughest challenges of the architecture.

Surrounding the Earth with satellite layers

The hypersonic defense architecture consists of three layers of satellites in low Earth orbit:

• A first layer of Wide Field of View (WFOV) satellites, that provide a persistent global coverage and are able to detect bright objects, like missiles in their boost phase. These satellites are also called OPIR for Overhead Persistent Infrared, but that is different from the high-altitude OPIR program.
• They will cue a second layer of Medium Field of View (MFOV) satellites, also called HBTSS for Hypersonic and Ballistic Tracking Space Satellites, which will be able to maintain a track of faint objects (for instance reentry vehicles and hypersonic gliders). They will trade the smaller field of view for a much more accurate and sensitive sensor, able to give a precise enough target position to be used to guide interceptors towards the tracked missiles. These satellite will also be able to perform other functions, like Space Situational Awareness, or Measurement and Signature INTelligence (MASINT).
• A transport layer, transmitting information from the WFOV satellites to the MFOV, and also relaying the information to the ground, both to integrated command and control (C2) systems using IBS messages in the Ka band, and also directly to individual platforms using the link 16 standard. It will use optical satellite cross-links.
• SDA is also developing another layer with an offensive role, to go after the enemy launchers (among other things). This layer, called the custody layer, will keep track of mobile ground and surface targets. It will likely consist mostly of radar SAR satellites, because they can operate at night and in all weather, whereas optical satellites cannot. Such a layer will provide the Persistent Surveillance enabled by Smallsat constellations.)
• Finally as position, navigation and timing layer is planned, to avoid relying on a handful of GPS satellites in MEO. It will probably exploit the accurate ranging and time-keeping capabilities offered by the optical crosslinks.

A battle management system (BMC3) with compute capability to run software (for instance for target detection and shooter allocation) directly in the constellation will be embedded in the tracking and transport satellites.

Regarding the timeline for deploying these constellations, procurement is underway, with some Request From Proposal (RFP) having already been issued to the industry. The first WFOV payloads have been contracted, the RFP for the bus should be issued shortly.

• In March 2021, a prototype WFOV payload will be launched to collect scene background data.
• Later in 2021, 3 WFOV payloads will be launched.
• In 2022, the first 8 WFOV satellites (tracking tranche 0) launch onboard a DARPA Blackjack launch
• Between 2022 and 2024, the transport tranche 0, consisting of tens of satellites, will launch.
• In 2023, the first MFOV satellites launch. They will demonstrate the integrated operation of MFOV, WFOV and the transport layer.
• In 2024, the tracking tranche 1, consisting of around 70 MFOV and WFOV satellites, launches. It will be spread geographically all over the globe, but because of power generation constraints aboard the satellites, will not be able to provide coverage on a full orbit. However it will be able to provide persistent surveillance of a regional area.
• In 2016, tranche 2 launches, which will provide global persistent coverage thanks to the additional satellites.

Organizational challenges

There are a lot of actors involved in this: DARPA, the newly formed Space Development Agency (SDA), the Missile Defense Agency (MDA), the armed services including the Space Force, the combatant commands, and possibly the intelligence community and the NRO for the custody layer. That would seem to be ripe for a “Pentagon Wars“-style exercise in miscommunication, over-specification and infighting. However, the project seems to be going smoothly on a very quick timeline. The speakers in the missile defense advocacy alliance video above emphasize a good communication between SDA and MDA, with SDA having the design authority over the constellation, but MDA providing the sensor design, the requirements and being in charge of ground dissemination and of the overall missile defense architecture. SDA enjoys strong political support in the administration, being the brainchild of former NASA administrator Mike Griffin, now under secretary of defense for research and engineering. It also has adopted the approach that good enough now is better than perfect tomorrow, and this is moving as fast a possible with demonstrators and initial capabilities in all layers, while synchronizing with the services on what threats will come online when to prioritize developments.

Another strength in the approach is that it piggybacks on the developments in small satellites and satellite constellations in the commercial sector, therefore using mature technology with a broad industrial base. New, riskier technologies are to be incorporated as they become reliable, in an incremental improvement approach at the constellation level. Every two years, a new “spiral” will be introduced, leveraging technological improvements and bringing new capabilities, while staying backward compatible with the satellites already on orbit.

A view of the future

With the SDA-developed proliferated LEO architecture, the USA are set to increase the resilience of their space systems, by not relying on a handful of multi-billion “silver bullet” satellites, and to revolutionize its capabilities. If the project goes well, they will field a very high bandwidth communication system, a missile detection and tracking system that will markedly improve their missile warning and defense, and a persistent surveillance system able to keep an eye on enemy high-value units.

While this may seem to be a Star Wars, Reagan-era bluff or pipe dream, it is not. The technology is proven, as many commercial companies design and produce small satellite buses and components, optical crosslinks and remote sensing payloads. The full constellation will confer a very hard-to-counter military advantage to the USA. The best shot their adversaries might have is to field a soft-kill anti-satellite system, to avoid creating debris and not spend more money per shot that the target is worth.