Proceedings of the 1996 IEEE International Frequency Control Symposium

Extremely large telescopes will be constructed in the near future, and new radiotelescopes will operate at considerably higher radio frequencies; both features create significantly increased pointing accuracy requirements that have to be addressed by control system engineers. This paper presents control and pointing problems encountered during design, testing, and the operation of antennas, radiotelescopes, and optical telescopes. This collection of challenges informs of their current status, helps to evaluate their importance, and is a basis for discussion on the ways of improvement of antenna pointing accuracy

Control and Pointing Challenges of Large Antennas and Telescopes

Atomic clocks, which lock the frequency of an oscillator to the extremely stable quantized energy levels of atoms, are essential for navigation applications such as deep space exploration1 and global navigation satellite systems2, and are useful tools with which to address questions in fundamental physics3–6. Such satellite systems use precise measurement of signal propagation times determined by atomic clocks, together with propagation speed, to calculate position. Although space atomic clocks with low instability are an enabling technology for global navigation, they have not yet been applied to deep space navigation and have seen only limited application to space-based fundamental physics, owing to performance constraints imposed by the rigours of space operation7. Methods of electromagnetically trapping and cooling ions have revolutionized atomic clock performance8–13. Terrestrial trapped-ion clocks operating in the optical domain have achieved orders-of-magnitude improvements in performance over their predecessors and have become a key component in national metrology laboratory research programmes13, but transporting this new technology into space has remained challenging. Here we show the results from a trapped-ion atomic clock operating in space. On the ground, NASA’s Deep Space Atomic Clock demonstrated a short-term fractional frequency stability of 1.5 × 10−13/τ1/2 (where τ is the averaging time)14. Launched in 2019, the clock has operated for more than 12 months in space and demonstrated there a long-term stability of 3 × 10−15 at 23 days (no drift removal), and an estimated drift of 3.0(0.7) × 10−16 per day. Each of these exceeds current space clock performance by up to an order of magnitude15–17. The Deep Space Atomic Clock is particularly amenable to the space environment because of its low sensitivity to variations in radiation, temperature and magnetic fields. This level of space clock performance will enable one-way navigation in which signal delay times are measured in situ, making near-real-time navigation of deep space probes possible18. Operating in space, NASA’s Deep Space Atomic Clock, a trapped-ion clock, is shown to have long-term stability and drift that are an order of magnitude better than current space clocks.

Demonstration of a trapped-ion atomic clock in space

Proceedings of the 1998 IEEE International Frequency Control Symposium

Space offers unique experimental conditions and a wide range of opportunities to explore the foundations of modern physics with an accuracy far beyond that of ground-based experiments. Space-based experiments today can uniquely address important questions related to the fundamental laws of Nature. In particular, high-accuracy physics experiments in space can test relativistic gravity and probe the physics beyond the Standard Model; they can perform direct detection of gravitational waves and are naturally suited for investigations in precision cosmology and astroparticle physics. In addition, atomic physics has recently shown substantial progress in the development of optical clocks and atom interferometers. If placed in space, these instruments could turn into powerful high-resolution quantum sensors greatly benefiting fundamental physics. We discuss the current status of space-based research in fundamental physics, its discovery potential, and its importance for modern science. We offer a set of recommendations to be considered by the upcoming National Academy of Sciences' Decadal Survey in Astronomy and Astrophysics. In our opinion, the Decadal Survey should include space-based research in fundamental physics as one of its focus areas. We recommend establishing an Astronomy and Astrophysics Advisory Committee's interagency "Fundamental Physics Task Force" to assess the status of both ground- and space-based efforts in the field, to identify the most important objectives, and to suggest the best ways to organize the work of several federal agencies involved. We also recommend establishing a new NASA-led interagency program in fundamental physics that will consolidate new technologies, prepare key instruments for future space missions, and build a strong scientific and engineering community. Our goal is to expand NASA's science objectives in space by including "laboratory research in fundamental physics" as an element in the agency's ongoing space research efforts.

http://inspirehep.net/record/766994/files/arXiv:0711.0150.pdf

Space-based research in fundamental physics and quantum technologies

An engineering prototype linear ion trap frequency standard (LITS-4) using /sup 199/Hg/sup +/ is operational and currently under test for NASA's Deep Space Network (DSN). The DSN requires high stability and reliability with continuous operation. For practical considerations optical pumping and atomic state selection are accomplished with a /sup 202/Hg/sup +/ RF discharge lamp, and the trapped ions are cooled to near room temperature using a helium buffer gas. The standard is closely modeled from earlier research standards LITS-1 and LITS-2 which have demonstrated excellent frequency stability for uninterrupted comparison intervals up to 5 months. During an initial 135 day test in the DSN, LITS-4 operated continuously using a quartz crystal as the local oscillator. Recent signal to noise measurements indicate that a short term stability of /spl sigma//sub y/(/spl tau/)=2.0/spl times/10/sup -14///spl tau//sup 1/2/ can be achieved when operated with a sufficiently stable local oscillator.

A mercury ion frequency standard engineering prototype for the NASA deep space network

RACE is a high performance Rb clock slated to fly on the International Space Station. RACE aims to realize high accuracy and short-term stability. The cold collision shift and multiple launching (juggling) have important implications for the design and the resulting clock accuracy and stability. We present and discuss the double clock design for RACE. This design reduces the noise contributions of the local oscillator and simplifies and enhances an accuracy evaluation of the clock.

RACE: laser-cooled Rb microgravity clock

A nonintrusive technique has been used to conduct a radial survey in the flow field of an arcjet engine plume. The technique measures the Doppler shift of an optically thin line resulting from recombination and relaxation processes in the high Mach number stream, in order to determine flow velocities. Atom temperature can also be calculated from the same Doppler-broadened line widths, when these shifts are measured with a scanning Fabry-Perot spectrometer whose design is presented in detail.

Velocity measurements in the plume of an arcjet engine

An engineering prototype linear ion trap fiequency standard (LITS-4) using '%g+ is operational and currently under test for NASA's Deep Space Network (DSN). The DSN requires hgh stability and reliability with continuous operation. For practical considerations optical pumping and atomic state selection are accomplished with a 2MHg+ RF discharge lamp, and the trapped ions are cooled to near room temperature using a helium buffer gas. The standard is closely modeled from earlier research standards LITS-l and LITS-2 whch have demonstrated excellent frequency stability for unintempted comparison intervals up to 5 months. Dliring an initial 135 day test in the DSN, LITS-4 operated continuously using a quartz crystal as the local oscillator. Recent signal to noise measurements indicate that a short term stability of ~,(z)=2.0xlO~~~/ ~.~~ can be achieved when operated with a sufficiently stable local oscillator.

For the nasa deep space network

We have begun constructing all-solid-state laser systems at 778 nm and at 532 nm in support of a satellite-based gravity-mapping mission tentatively planned to fly in 2007 In each case the lasers will be stabilized at short times to high-finesse Fabry-Perot cavities At longer times the 778 nm laser will be stabilized to the 2-photon transition in rubidium In the 532 nm system, a frequency-doubled Nd:YAG laser with a non-planar ring oscillator (NPRO) design will be frequency-locked to a molecular iodine line We intend to combine the exquisite performance over short time scales coming from a cavity reference with the long-term stability of an atomic frequency standard with an eye towards reliability in a spaceflight application By developing two separate candidate systems with proven performance we intend to maximize the probability of success for this mission-critical system development

Optical frequency standard development in support of NASA's gravity-mapping missions

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

D.J. Seidel

Author Tools

Chat about Author