LAGRANGE: LAser GRavitational-wave ANtenna at GEo-lunar Lagrange points (1111.5264v2)

Abstract: We describe a new space gravitational wave observatory design called LAGRANGE that maintains all important LISA science at about half the cost and with reduced technical risk. It consists of three drag-free spacecraft in the most stable geocentric formation, the Earth-Moon L3, L4, and L5 Lagrange points. Fixed antennas allow continuous contact with the Earth, solving the problem of communications bandwidth and latency. A 70 mm diameter AuPt sphere with a 35 mm gap to its enclosure serves as a single inertial reference per spacecraft, which is operated in "true" drag-free mode (no test mass forcing). This is the core of the Modular Gravitational Reference Sensor whose other advantages are: a simple caging design based on the DISCOS 1972 drag-free mission, an all optical read-out with pm fine and nm coarse sensors, and the extensive technology heritage from the Honeywell gyroscopes, and the DISCOS and Gravity Probe B drag-free sensors. An Interferometric Measurement System, designed with reflective optics and a highly stabilized frequency standard, performs the inter-test mass ranging and requires a single optical bench with one laser per spacecraft. Two 20 cm diameter telescopes per spacecraft, each with in-field pointing, incorporate novel technology developed for advanced optical systems by Lockheed Martin, who also designed the spacecraft based on a multi-flight proven bus structure. Additional technological advancements include the drag-free propulsion, thermal control, charge management systems, and materials. LAGRANGE sub-systems are designed to be scalable and modular, making them interchangeable with those of LISA or other gravitational science missions. We plan to space qualify critical technologies on small and nano satellite flights, with the first launch (UV-LED Sat) in 2013.

• The paper presents a novel mission concept using three spacecraft at Earth-Moon Lagrange points to detect gravitational waves, paralleling LISA's capabilities at reduced cost.
• The methodology employs a single spherical test mass in a drag-free setup and an advanced interferometric measurement system to achieve high precision.
• The design leverages modular architecture and heritage technologies from missions like Gravity Probe B to minimize operational risks and simplify mission complexity.

Overview of the LAGRANGE Mission Concept

The paper "LAGRANGE: LAser GRavitational-wave ANtenna at GEo-lunar Lagrange points" presents a novel design for a space-based gravitational wave observatory. Formulated by a consortium of researchers from institutions such as Stanford University, NASA Ames, and Lockheed Martin, the LAGRANGE mission offers an innovative approach to gravitational wave detection by leveraging the stable environment of Earth-Moon Lagrange points (L3, L4, L5). This configuration aims to replicate the scientific capabilities of the Laser Interferometer Space Antenna (LISA) mission while significantly reducing costs and technical risks.

Key Features and Innovations

1. Mission Architecture:
   • The LAGRANGE observatory consists of a triangular constellation of three identical spacecraft positioned at the Earth-Moon Lagrange points L3, L4, and L5. This stable geocentric configuration allows for reduced complexity in propulsion and data transmission.
   • A Falcon 9 vehicle is proposed for launching all three spacecraft with a single propulsion module, leveraging its cost-effectiveness.
2. Gravitational Reference Sensor (GRS):
   • Each spacecraft houses a single spherical test mass in a "true" drag-free setup. The design is influenced by technologies from the DISCOS mission and Gravity Probe B.
   • The GRS utilizes a Modular Gravitational Reference Sensor (MGRS) that is characterized by its simplicity and no test mass forcing—an advancement aimed at reducing disturbances and operational risks.
3. Interferometric Measurement System (IMS):
   • A single optical bench per spacecraft, equipped with a laser and telescopes, is used for precise measurement of gravitational waves. The IMS employs reflective optics and benefits from Lockheed Martin's prior developments.
   • Novel frequency stabilization techniques are employed alongside telescopically guided beam steering mechanisms to enhance observation precision.
4. Technological Synergies and Reductions:
   • Considerable cost savings are realized by decreasing component redundancy—reducing from two lasers, GRS, and optical benches per spacecraft in LISA to one each in LAGRANGE, without compromising sensitivity.
   • The geocentric orbit reduces the complexity of mission operations, enabling a significant increase in communication bandwidth compared to LISA.

Scientific and Technical Implications

The LAGRANGE mission is poised to contribute substantially to the field of gravitational wave astronomy with sensitivity spanning from 1 mHz to 1 Hz. This range covers significant astrophysical phenomena, including black hole mergers and exotic sources potentially observable in the early universe. By achieving these goals with reduced resource commitments compared to LISA, the LAGRANGE mission offers a viable alternative for long-term gravitational wave monitoring.

The theoretical significance of LAGRANGE lies in its modular and scalable architecture, which could serve as a template for future gravitational wave missions. Practically, leveraging the stable Lagrange point orbits allows for more efficient mission planning and execution, potentially opening new avenues for deep-space exploration technologies.

Future Prospects

Assuming successful demonstration and deployment, LAGRANGE's approach could influence the design philosophy for a range of future space missions. Its emphasis on modular technology and leveraging heritage systems from earlier missions are likely to set a precedent in achieving efficient cost-performance balances in space observatories.

In conclusion, LAGRANGE represents a strategic endeavor to advance the capabilities of space-based gravitational wave research. It integrates heritage technologies with innovative design, positioning it as a potentially influential mission within the astrophysics and aerospace communities. Collaborations observed in LAGRANGE could expand, involving international partnerships and creating a synergy for broader scientific exploration. The initiatives started here might pave the way for more accessible and frequent access to the cosmos through similar mission architectures.