astronomy

XTAR

XTAR is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand XTAR rather than just read about it. In short: XTAR, LLC is a US-based company founded in 2001 for the purposes of commercializing the capacity and services on HISDESAT’s governmental satellite systems, which are purpose-built to meet the needs of the Kingdom of Spain. XTAR provides military satellite communications (MILSATCOM) capacity and services in X-, mil-Ka, and UHF-frequency bands.

Key takeaways

XTAR belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect XTAR to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of XTAR from memory before moving on to harder problems.

Reference excerpt

XTAR, LLC is a US-based company founded in 2001 for the purposes of commercializing the capacity and services on HISDESAT’s governmental satellite systems, which are purpose-built to meet the needs of the Kingdom of Spain. XTAR provides military satellite communications (MILSATCOM) capacity and services in X-, mil-Ka, and UHF-frequency bands. It also provides all-weather, high-resolution .X-band synthetic aperture radar (SAR) imaging/earth observation services to the US Department of Defense, NATO Allies, and partner nations as well. Roles:

HISDESAT has a Public-Private Partnership with the Spanish Ministry of Defense, and thus acquires and operates the satellites, and provides the services required by them. Together, XTAR and Hisdesat provide the capacity unused by the Spanish Ministry of Defense to other NATO Allies and partner nations.

Mission Founded in 2001, U.S.-based XTAR was the world's first commercial satellite operator to provide services to government end-users on NATO Allied MILSATCOM assets, which today form the communications cornerstone of today's military, diplomatic, humanitarian and emergency disaster response operations. In 2024, HISDESAT expanded XTAR's role to also provide synthetic aperture radar (SAR) earth observation services to the US Department of Defense and other NATO Allies and partners. A privately owned and operated U.S. company, XTAR today supports the critical satellite communications and earth observation needs of governments around the world through both its MILSATCOM and SAR imaging services. Loral Space & Communications, Inc. owns the majority share. XTAR is headquartered in Leesburg, VA. XTAR bandwidth is not application-specific; it can support and transmit to any one of the primary architectures used by government agencies today, including fixed-to-fixed, tactical-to-tactical, reach-back, broadcast and airborne platforms. In 2019, XTAR and Spanish governmental satellite operator Hisdesat announced plans to construct two new military communications satellites. The new 'Next Generation' satellites have X, mil-Ka, and legacy UHF payloads and will be launching in 2025.

Satellite fleet

Legacy satellites (2005-2026) 4 GB of circular polarity X-band capacity 72 MHz transponders Coverage from 105 degrees West Longitude east to 120 degrees East Longitude Global, fixed and steerable spot beams Right hand and Left hand circular polarity On-board switching enabled Compatible with existing X-band terminals Non-preemptible service Encrypted command and control links The XTAR legacy fleet uses the hosted payload model, an application that is becoming increasingly used by U.S. and other governments. XTAR-EUR hosts a payload and XTAR-LANT is a hosted payload. Both satellites are built on the SSL 1300 modular platform from Space Systems/Loral and designed for 18-plus years of on-orbit operation. The spacecraft attitude maintained to within 0.02° in roll, pitch, and yaw. With its high-powered 72 MHz transponders and global, fixed and steerable beams, XTAR provides 1.44 GB of secure X-band capacity with coverage from Denver east to Singapore. The system can accommodate massive wideband data requirements and provides overlapping coverage with regional redundancy for increased service and reliability. The legacy XTAR satellites were designed and built by private financing. Additional details:

XTAR-EUR

This satellite, at 29 degrees East longitude and originally owned by XTAR, began operations in February 2005. The XTAR-EUR satellite hosts a NATO-configurable payload designed to support an anchor European customer. The coverage area includes Eastern Brazil and the Atlantic Ocean, Europe, Africa, the Middle East, and Southeast Asia as far east as Singapore. Hisdesat and XTAR announced on July 31, 2020 that they completed a transaction whereby Hisdesat Strategic Services SA purchased the satellite from XTAR, mirroring Hisdesat's ownership of the XTAR-LANT/Spainsat satellite (immediately below), and thus simplifying the ownership arrangement of the two satellites.

XTAR-LANT XTAR-LANT is a hosted payload on the Spainsat satellite. The satellite, at 30 degrees West longitude, is owned by Hisdesat and was placed into orbit in 2006. The coverage area includes North America, South America, Europe, Africa, and the Atlantic Ocean.

Next-generation satellites (2025-present)

XTAR-EUR-NG ("NG1") and XTAR-LANT-NG ("NG2") On January 29, 2025, Hisdesat launched the "Next-Generation" replacement of XTAR-EUR. This on-orbit replacement, formally known as and filed with the ITU as "Spainsat-NG1," is commonly also referenced as "EUR-NG" or "NG1," and will arrive on-orbit in Aug/Sep 2025. Its twin, known as "Spainsat-NG2" (or "LANT-NG" or "NG2") is scheduled for launch in summer 2025 and will arrive on orbit to replace XTAR-LANT in Feb/Mar 2026. Together, these two fully software-defined satellites will be the most advanced satellites of their kind over Europe: Features:

6 GHz of X-band, 2 GHz of mil-Ka band, and 9 x 25-kHz wide channels of legacy (non-WCDMA) capacity per satellite Highly-efficient, DRA phased-array X-band antennas with on-board processing supports rapid geolocation, nulling, and RF muting, with shapeable beams ranging from 2.2-degrees to satellite FOV 6 steerable parabolic, and 1 non-steerable semi-global, mil-Ka antennas per satellite, with RF muting . Digital channelizers with cross-banding and flexible power allocation between X- and mil-Ka payloads; supports carriers 312.5 kHz to 500 MHz wide (X-band) and up to 1 GHz wide (mil-Ka), so suitable for today's most advanced waveforms Coverage from 105 degrees West Longitude east to 120 degrees East Longitude X-band in Right hand and Left hand circular polarity; mil-Ka is Right hand only NATO CP-130 MILSATCOM/SAL-3 Compliant NATO SATCOM Services - 6th Generation (NSS6G) Member Works with all NATO CP-130-compliant MILSATCOM terminals (i.e. WGS terminals) Non-preemptible service Encrypted command and control links to NATO standard

SAR imaging satellite

Earth Observation Satellite "PAZ"

Launched in 2018 from Vandenburg SFB, California, the Spanish MoD's "PAZ" (or "Peace") satellite provides high-resolution, all-weather X-band imaging services that are totally independent of weather. While ostensibly designed for Spanish MoD purposes, this advanced X-band imaging satellite can and does support a wide variety of civil and military applications today. Key features:

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with XTAR

Start with the simplest possible case. Write down what XTAR claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to XTAR before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about XTAR ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of XTAR

In research: XTAR appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses XTAR in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: XTAR is common in secondary-school and first-year university syllabi. It links to neighbouring topics Communications satellite operators, Communications satellites in geostationary orbit, Companies based in Virginia, so understanding it makes those chapters shorter.
In everyday life: Look for XTAR outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “XTAR” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study XTAR in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what XTAR means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain XTAR out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is XTAR in simple terms?

Why does XTAR matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study XTAR?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on XTAR.